Join Date: Mar 2013. Following example proves the same. (1.) Top Forums Shell Programming and Scripting Check if a string exists in a file # 1 07-23-2015 kraljic. In bash, ksh or zsh: In my last article I shared some examples to get script execution time from within the script.I will continue with articles on shell scripts. The following script will store the updated content in the temp.txt file that will be renamed by the original file. How do I find out filename (mysql.tgz) and extension (.tgz) in bash program running under Linux or Unix operating systems? However, they all generally work quite similarly, so we'll still be able to help you out. Use -f switch with the if condition to check if a file exists. Posts: 5 Thanks Given: 0. While creating a bash script, it is commonly helpful to test if file exists before attempting to perform some action with it.. On GUI, most text editors also have the ability to search for a particular string. If you want to search multiple files, just append as many to the command as you'd like. Terminal Output . How to check if a filename in a directory starts with a certain string Hello, Trying to iterate over set of file in current directory and check if the file name in that folder matches certain string. The string to check. Q. In this tutorial, we shall learn how to compare strings in bash scripting. The command ‘mv’ is the most popular command for renaming a file. So say I have these files: Assigned_1day_after_due_chuong Assigned_1day_after_due_gallen Assigned_1day_after_due_heidenre and i'm running a script and want to know if a file exists with "chuong" in the name. Aqsa Yasin in the terminal as displayed in the appended image. After storing my username I am not too sure on the best approach to check to see if it already exists. The -z operator functions similarly like -n operator. Check if the string is empty. "tasks:") if found or else the name of the file. After word splitting, unless the -f option has been set (see The Set Builtin), Bash scans each word for the characters ‘*’, ‘?’, and ‘[’. If you've already opened a file in a command line or GUI editor, there are search functions available there as well. The UNIX and Linux Forums. In this example, we shall check if two string are equal, using equal to == operator. The issue you are having is due to the fact that _ is a valid character in a variable name. For example, the filenames are in xyz.abc.d.CSV format. The output from grep shows us which files the string was found in. Thanked 0 Times in 0 Posts Check if the string is empty. I have included some of the most popular test conditions in the table below: e.g. Suggestions? The basename command strip directory and suffix from filenames. As you can see from the screenshot, grep returns the entire line that contains the word "example." Bash – Check if Two Strings are Equal. Bash Compare Strings. Below is an example: n operator to check if string is empty. In this Bash Tutorial, we shall present you with syntax and examples to read a file.. In this guide, you learned everything you'll need for finding a text string in one or more files on Linux. Many commands exist in Linux to rename a filename. So the output will be Hy! BASH scripting: check for numeric values I have a script that I've made which takes two arguments: a pure number and a filename. Test conditions varies if you are working with numbers, strings, or files. In Bash you can use the test command to check whether a file exist and determine the type of the file. Thanked 0 Times in 0 Posts bash: testing if string is a number. Type: string. Replace String in a File with `awk` Command. For example: I have a text file with information in the format of /etc/passwd. str1 = "tutorialkart" str2 = "tutorial" if [ $ str1 != $ str2 ]; then echo "Two strings are not equal." If you just want to output the pathname of the file, then use. check if a given string is a file or directory. Bash Function. Bash String. Forums. Check if a string exists in a file. On the other hand, if the string is empty, it won’t return true. The matching does not produce the right results Search files for a text string via command line, 2. Bash Read File – To read a file in Bash Scripting, you may use cat command or use “<” to open file and attach it to a standard input device handle of some application. I'm trying to do a simple if statement that tests if a filename exists with a user specified string. Example 4: Replace File with ‘awk’ Command. Example 1 In the following example, we use ${#string_variable_name} to find string length. While creating a bash script, it is commonly helpful to test if file exists before attempting to perform some action with it.. You could also specify a directory in your command, but omitting it (as we did in this example) will instruct grep to search every directory in the current path. 5, 0. When writing Bash scripts you will often need to compare two strings to check if they are equal or not. Swag is coming back! If you have a file opened in nano and need to find a particular string, there's no need to exit the file and use grep on it. h0ujun: View Public Profile for h0ujun: Find all posts by h0ujun # 2 02-16-2012 kalpeer. shell scripts Thread Tools: Search this Thread : Top Forums Shell Programming and Scripting bash: testing if string is a number # 1 07-19-2006 eur0dad. input. LinuxConfig is looking for a technical writer(s) geared towards GNU/Linux and FLOSS technologies. How do I check if a specified file exists or not? To search a file (or files) for a particular text string, the only command you should need to know is grep. bash in RHEL 6.3 I have these 2 files with strings. Linux Users. eg. Furthermore, the bash manual warns that this sort of pattern matching is slow if the string which should be matched is long. 157, 25. When -n operator is used, it returns true for every case, but that’s if the string contains characters. In this tutorial, we have example bash scripts to demontrate on how one can check if file has read premissions. Thanked 1 Time in 1 Post Check if a string exists in a file. Following are the examples that demonstrate different ways to find the string length in bash shell scripting. The $ character is used for parameter expansion and command substitution. grep -lF 'string' file1.txt test2.txt file23.txt tact24.txt The syntax is pretty simple: basename /path/to/file basename /path/to/file suffix. You should print a certain message if true and another if false. Bash has a built-in simple pattern matching system. To search a file for a text string, use the following command syntax: For example, let's search our document.txt text document for the string "example.". Man. as the current directory. This is a synonym for the test command/builtin. Most importantly, you should add spaces around the square brackets. $ bash CheckStrings.sh. Registered User. Examples. empty string condition, shell scripts Thread Tools: Search this Thread : Top Forums Shell Programming and Scripting Check if the string is empty # 1 03-18-2013 nw2unx123. How to do group_concat in select query in Sequelize? next → ← prev. And it's easy enough to master. Registered User. To check if two strings are equal in bash scripting, use bash if statement and double equal to == operator. Related. Output . To check if string “Bus” stored in $vech starts with “B”, run: [ [ $vech = B* ]] && echo "Start with B" The [ [ used to execute the conditional command. It works as a "switch" statement in other languages (bash, zsh, and ksh93 also allows you to do fall-through in various incompatible ways). Compare Strings in Bash. The [and [[evaluate conditional expression. Miscellaneous. If other code forces the input to be a single character, it doesn't matter, but what the cooe actually does is to check that there is at least one matching character in a potentially longer string. Bash Array. The easy way to check that a string only contains characters in an authorized set is to test for the presence of unauthorized characters. Write conditions on strings: if a string variable is set or if two strings are equal to each other. Let's get started by working with the most simple forms of the command and getting gradually more complex. 121, 1. Join Date: Jan 2009. Your articles will feature various GNU/Linux configuration tutorials and FLOSS technologies used in combination with GNU/Linux operating system. Example – Strings Equal Scenario The reason is that, in bash, brace expansion (i.e., {pattern1,pattern2,...} and filename expansion (a.k.a. How to add a custom column which is not present in table in active admin in rails? As our string StdName has now a value Aqsa Yasin, so the -n string operator executed the if part. Bash Arrays. Thus, instead of testing whether the string only contains spaces, test whether the string contains some character other than space. [duplicate]. -n is one of the supported bash string comparison operators used for checking null strings in a bash script. You'll learn how to use the grep command to perform this task, as well as how to access the search function in command line and GUI text editors. Bash script to sort files into folder according to a string in the filename I am very new to linux scripting and i have a task i can only solve with a script. You can also use … The expression returns true if the file is readable and false if the file is not readable. If the string is simply the filename, dirname will print a (.) The patterns used are the standard file name globbing patterns. Instinctively you think that this "language" requires you to follow an if with a [or a [[.Both of those are just commands that return an exit status indicating success or failure (just like every other command). 1. On a Linux system, the need to search one or multiple files for a specific text string can arise quite often. Install $ npm install valid-filename Usage. This tutorial describes how to compare strings in Bash. Details Use == operator with bash if statement to check if two strings are equal. Search a file for a text string via GUI, How to create compressed encrypted archives with tar and gpg, Ubuntu 20.04 Burn ISO to DVD from command line, Privileged access to your Linux system as root or via the, How to search files for a text string via command line, How to search files for a text string via command line text editors, How to search a file for a text string via GUI text editors. Here I am checking if the file name starts with nexus, if so echo file name to log file. When writing Bash scripts you will often need to compare two strings to check if they are equal or not. The way I have written the sub() command, it would retain the directory path of the file if this was given on the command line. The [and [[evaluate conditional expression. – tripleee Jul 1 '17 at 10:58 Example : Bash Read File using – cat fileName … Getting weird syntax errors. Today's Posts. Bash Strings Equal – In this tutorial, we shall learn how to check if two strings are equal in bash scripting. Different distros and desktop environments have their own software, so it's impossible to write a guide that will cover them all. instead of re-inventing the wheel, use the following tools: sort and uniq to keep duplicated lines only. Bash Script Examples are provided to check if file exists. If there are no spaces, bash will complain about that. Bash get filename from given path. Two strings are not equal. Multiple Left Joins in MS Access using sub-queries. Related. Let's get started by working with the most simple forms of the command and getting gradually more complex. Linux Processes. So in the example above since bob appears twice my output would simply generate something like: Right now I have a while loop that reads each line and stores each piece of information in a variable using awk -F that is delimited with ":". All you need to do is type :/ followed by your search string, then press Enter. In this tutorial I will cover different attributes you can use in bash or shell scripting to check against files and directories. bash if -z #!/bin/bash . Search. : 'ab' in 'abc' -> true 'ab' in 'bcd' -> false How can I do this in a conditional of a bash script? However, [[is bash’s improvement to the [command. Tags. I need to sort files base on the date string in their filenames and create a folder using the same date string then move the files to their respective folders. To check if two strings are not equal in bash scripting, use bash if statement and not equal to!= operator. In this example, we shall check if two string are not equal, using not equal to != operator. [-e FILE] is preferred as [-a FILE] is depreciated. 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This shell script accepts two string in variables and checks if they are identical. Posts: 8 Thanks Given: 0. Example 4: Replace File with ‘awk’ Command. and uniq to keep duplicated lines only. To check if two strings are equal in bash scripting, use bash if statement and double equal to == operator.. To check if two strings are not equal in bash scripting, use bash if statement and not equal to!= operator.. The ‘awk’ command is another way to replace the string in a file, but this command cannot update the original file directly like the ‘sed’ command. I decided to give it a little bit of flexibility and have it so that it doesn't matter what order those two arguments are put: number then file name, or file name … glob patterns) are considered separate things and expanded under different conditions and at different times. How to check if a string begins with some value in bash . To Check if a file is readable using Bash script, use [ -r FILE ] expression. I am new to shell scripting and I can't figure it out on how to check the filenames if it has a specific string. Bash Write to a File. The vim text editor also has a built-in method for searching for a string. If your string has to check both, check for letters and then check for numbers (or reverse order) . Anyone can easily rename a file by using the graphical user interface (GUI). Bash If File Exists - You can check if file exists in bash scripting with the help of [ -a FILE ] and [ -e FILE ] expressions in conjunction with bash if statement. Tags. As you can see, grep searched multiple directories and indicates where it found the string. bash: testing if string is a number. Think of them as logical operators in bash. Note: Your filename can be anything but for this article, we will be using “file name.txt” as an example.. Bash Strings Equal. If you do quote the right hand side "Any part of the pattern may be quoted to force it to be matched as a string." Type the following basename command: basename /bin/ls You can pass multiple arguments using the -a option as … Bash Read File Bash Write File Check if file Exists Check if Variable is Set Bash Alias Git Bash Zsh vs Bash Bash Hash Command. instead of re-inventing the wheel, use the following tools: cut to extract first field; sort and uniq to keep duplicated lines only. And it's easy enough to master. Please note that the following is bash specific syntax and it will not work with BourneShell: Two strings are equal when they have the same length and contain the same sequence of characters. If the file is available in the specified location then while loop will read the file line by line and print the file content. The grep command proves very wieldy and can fetch results lightning quick. I want to simply check if there are duplicate users and if there are, output the line to standard error. Checking if a string contains a substring is one of the most basic and frequently used operations in Bash scripting. On the command line, the grep command has this function covered very well, but you'll need to know the basics of how to use it. The command will check all files in the directory with txt extension and either write the search string (i.e. Bash String Bash Find String Bash Split String Bash Substring Bash Concatenate String. Bash Read File. One can test that a bash variable starts with a string or character in bash efficiently using any one of the following methods. if [ -z "" ]; then echo "zero length string" fi . Join Date: Oct 2011. bash-strings-equal #!/bin/bash . Two strings are equal when they have the same length and contain the same sequence of characters. Bash – Check If Two Strings are Equal Brief: This example will help you to understand to check if two strings are equal in a bash script. shell scripts. Then execute a set of statement if a file exists: Check if a file exists: If you often create Bash scripts, you may sometimes need to get the length of a string or find out the length of a variable that stores some string.. Example: To return the absolute path change the script's directory. 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Last Activity: 21 November 2019, 2:25 AM EST . You can also use wildcards in the commmand. You can use bash conditional expressions with [[ ]] or use test with [ ] to check if file exists.. We will be using bash if and else operator for all the examples so I would recommend you to read: Bash if else usage guide for absolute beginners It checks if $vech starts with “B” … Featured on Meta New Feature: Table Support. make sure to always put the regular expressions on the right un-quoted and (2.) On our Ubuntu test machine, we're running GNOME and have access to the text editor simply known as "text editor." Hello, Trying to iterate over set of file in current directory and check if the file name in that folder matches certain string. pre { overflow:scroll; margin:2px; padding:15px; border:3px inset; margin-right:10px; } Code: \\$ ca | The UNIX and Linux Forums . Linux System Admin. Linux Commands . hi i want to know how to do this if the given is /tmp/ and it is a valid directory then it will echo directory if the given is /tmp/file.txt and is a valid file then it will echo file.. thanks! Create a Bash script which will print a message based upon which day of the week it is (eg. HowTo: Check If a String Exists Posted on Tuesday December 27th, 2016 Friday February 24th, 2017 by admin Sometimes, we need to check if the pattern presents in … Use of if -z when String is Null. Let us see how to extract a filename from given file such as /bin/ls. bash if -z : Check if String has zero length. Linux Shell. Then the wildcards around the condition are wrong. Bash – Check if Two Strings are Not Equal. There are numerous test conditions that you can use with if statements. share | improve this answer | follow | Please note that the following is bash specific syntax and it will not work with BourneShell: I want to see if a string is inside a portion of another string. -z is the second supported bash string comparison operator used to check if a string is empty or not. Registered User. Bash Read File. Spring Boot, static resources and mime type configuration, Python- How to make an if statement between x and y? Registered User. cat file name.txt Running the command without using escape character or quotations. You should remember that shell scripting is less of a language and more of a collection of commands. Here is the full list of expansions that bash performs: There are many ways that we can use to read a file in Bash Shell Scripting. To search recursively, use the -r option with grep. API validFilename(input) Returns a boolean of whether input is a valid filename. The first argument value is read by the variable $1, which will include the filename for reading. Searching files on Linux for a text string is a common task and it's one that's easy to master. However, [[is bash’s improvement to the [command. if [ -z "hello" ]; then echo "hello is zero length string" else echo "hello is not zero length string" fi . We can access its search function from the menu, as seen in the screenshot below. How to get numbers by using regular expression, but only last one. Bash File Conditions. 8, 0. Linux Files. I'm writing a script in UNIX where I have to check whether the first character in a string is "/" and if it is, branch. Conditions on django filter backend in django rest framework? Now we will run the below-mentioned command to check whether the string has some value or not. In this article i will share examples to compare strings in bash and to check if string contains only numbers or alphabets and numbers etc in shell script in Linux. Where are my Visual Studio Android emulators. There are tons of GUI text editors available for Linux. Create a bash and add the following script which will pass filename from the command line and read the file line by line. The following script will store the updated content in the temp.txt file that will be renamed by the original file. After reading this tutorial, you should have a good understanding of how to test whether a string includes another string. Quick Links Shell Programming and Scripting . Here ‘cat‘ command will consider file and name as two arguments rather than a single argument. Bash check if a string contains a substring . You can also rename a file by using a command in bash script. If you often create Bash scripts, you may sometimes need to get the length of a string or find out the length of a variable that stores some string.. 3.5.8 Filename Expansion • Pattern Matching : How the shell matches patterns. You can also use != to check if two string are not equal. Join Date: Jul 2006. Bash Script File. Help with script reading numbers from a file and determining if they are even or odd numbers . It will only read and execute commands from a given filename in the current shell enviroment. Check out our guide on grep for more in-depth information, or check the man page for more command line options. Bash check if a string contains a substring . Tags. Bash Script File Here are some other handy grep command options you may need when searching for a text string: There's still a lot more you can do with grep. I want to write a script to check for duplicates 1. This is what I … Replace String in a File with `awk` Command. Bash Strings Equal – In this tutorial, we shall learn how to check if two strings are equal in bash scripting.. Bash Strings Equal. Filename Expansion (Bash Reference Manual) Next: Quote Removal, Previous: Word Splitting, Up: Shell Expansions . Introduction – In bash, we can check if a string begins with some value using regex comparison operator =~. Last Activity: 9 May 2013, 1:22 PM EDT. valid-filename . It consists of a few wildcards: * – matches any number of characters + – matches one or more characters [abc] – matches only given characters For example, we can check if the file has a .jpg extension using a conditional statement: $ if [[ "file.jpg" = *.jpg ]]; then echo "is jpg"; fi is jpg If the string occurs on multiple lines, then all of those lines will be returned as well. you could check if the file is executable or writable. Just press Ctrl + W on your keyboard, type the search string, and hit Enter. Create a Bash script which will accept a file as a command line argument and analyse it in certain ways. To search a file for a text string, use the following command syntax: $ grep string filename Bash Functions. The ‘awk’ command is another way to replace the string in a file, but this command cannot update the original file directly like the ‘sed’ command. In this article, we'll show you how to quickly and easily search through files for a specified text string. Check if a string is a valid filename. Test conditions in bash. When checking if a file exists, the most commonly used FILE operators are -e and -f. The first one will check whether a file exists regardless of the type, while the second one will return true only if the FILE is a regular file (not a directory or a device). The filename suffix is anything after the first dot in the filename. if statement when used with option z , returns true if the length of the string is zero. 2. This is a synonym for the test command/builtin. Comparing strings mean to check if two string are equal, or if two strings are not equal. To search a file (or files) for a particular text string, the only command you should need to know is grep. You can quickly test for null or empty variables in a Bash shell script. Linux Advanced. ... Ciao Winter Bash 2020! Last Activity: 15 June 2007, 2:07 PM EDT. You need to pass the -z or -n option to the test command or to the if command or use conditional expression.This page shows how to find out if a bash shell variable has NULL value or not using the test command. Simple forms of the string is empty = to check if the file content the if condition to check a... Best approach to check if a file in bash scripting, use the test to... When the right un-quoted and ( 2. all of those lines will be using file... Appended image terminal as displayed in the appended image check to see if already! See, grep searched multiple directories and indicates where it found the has. Line or GUI editor, there are many ways that we can use with if.! Valid character in bash scripting ( s ) geared towards GNU/Linux and FLOSS technologies I. Used operations in bash shell script given file such as /bin/ls the basic. Or if two string in one or multiple files, just append many. Posts bash: testing if bash check if string is in filename has some value in bash script examples are provided check! We 'll still be able to help you out is read by the file. Which day of the week it is ( eg script will store the updated content in the image. Or multiple files, just append as many to the [ command it! A filename from the menu, as seen in the following script will store the updated in. With grep can arise quite often read premissions the type of the week it commonly! The next row from the command as you can also use … bash check if strings...: check if file exists are wrong to find the string contains characters are having due... 2 files with strings $ character is used for parameter Expansion and command substitution how shell! As our string StdName has now a value Aqsa Yasin in the temp.txt file that will renamed. The standard file name in that folder matches certain string various GNU/Linux configuration and!: bash read file using – cat filename … if the file line by line and the... And print the file is available in the appended image matches patterns improve this answer | |. All of those lines will be renamed by the original file you are having is due the. On your keyboard, type the search string, the bash manual warns that this sort of pattern matching how! Then while loop will read the file that 's easy to master django rest framework begins with value... Line options and desktop environments have their own software, so it impossible. Will often need to do group_concat in select query in Sequelize current enviroment! Access its search function from the menu, as seen in the following,! Extension (.tgz ) in bash compare strings in bash script do I check they. That shell scripting in 0 Posts bash: testing if string has some value in bash, static and! Another string use … bash check if a file as a command line options know is grep exists... Screenshot below can fetch results lightning quick 2:25 am EST anyone can easily rename a file using... And indicates where it found the string contains some character other than space am EST part! Software, so it 's impossible to write a guide that will be using “ file ”... Gnu/Linux operating system instead of re-inventing the wheel, use bash if statement check. Two arguments rather than a single argument only read and execute commands from a filename! Method for searching for a particular text string strings in a file in my last I... Else the name of the string contains some character other than space conditions on django backend. Patterns used are the standard file name to log file right results Suggestions command line and read file... Our guide on grep for more in-depth information, or files ) for a specified text string can quite! Upon which day of the week it is ( eg switch with the most basic and frequently used in... Not too sure on the other hand, if so echo file name to log.... The expression returns true for every case, but that ’ s improvement to the fact _. String are not equal to == operator true if the file name to log.... The text editor also has a built-in method for searching for a particular string file content thanked 1 Time 1. Answer | follow | then the wildcards around the square brackets, use [ -r file is... The appended image Profile for h0ujun: View Public Profile for h0ujun: find all by... Bash script equal when they have the ability to search for a contains... Perform some action with it to get script execution Time from within script.I! The command line argument and analyse it in certain ways Linux to rename a by. [ -a file ] is preferred as [ -a file ] is depreciated bash will about... By your search bash check if string is in filename, the filenames are in xyz.abc.d.CSV format storing username. In bash you will often need to compare two strings are equal or! Echo file name in that folder matches certain string you want to simply if! Only command you should remember that shell scripting validFilename ( input ) returns a boolean whether... “ file name.txt ” as an example: n operator to check if string is a valid filename grep... Temp.Txt file that will be returned as well to help you out which day of the name... Find all Posts by h0ujun # 2 02-16-2012 kalpeer if found or else the of! Get numbers by using the graphical user interface ( GUI ) to compare strings in program. Conditions and at different Times search a file by using a command line options name.txt running the command and gradually. 'Ve already opened a file ( or files ) for a text via! To add a custom column which is not readable using escape character or quotations and uniq to keep duplicated only... The first dot in the following tools: sort and uniq to keep duplicated lines only -n is one the. Ways that we can access its search function from the table program running under Linux or operating... Conditions that you can use to read a file by using regular expression, only... To == operator via command line and print the file name to log file about that false if string! More of a language and more of a language and more of a collection of commands test command to if! Use $ { # string_variable_name } to find the string is empty it. String was found in statement and double equal to == operator in RHEL I. And determining if they are equal when they have the ability to a! The matching does not produce the right un-quoted and ( 2. you! All Posts by h0ujun # 2 02-16-2012 kalpeer a Linux system, the only you... Switch with the if part grep shows us which files the string contains a substring is one of the.. But for this article, we shall learn how to add a custom column which not... Be returned as well one of the command line or GUI editor, are... Manual warns that this sort of pattern matching is slow if the file is... If two string are equal, using not equal to == operator are equal using. 'S directory specified text string value is read by the variable $ 1, which will print a message upon! Search recursively, use bash if statement when used with option z, returns true if the length!: to return the absolute path change the script 's directory read the file globbing.. 'Re running GNOME and have access to the [ command, we shall check if strings! Set of file in bash efficiently using any one of the string inside. Used, it won ’ t return true all you need to compare two strings are not equal that... Shell enviroment also rename a file Ctrl + W on your keyboard, type the search string and... It already exists that ’ s improvement to the command ‘ mv is! Not present in table in active admin in rails see how to compare strings in a command line and the! To find string bash Split string bash substring bash Concatenate string users bash check if string is in filename if are. Use … bash check if two string in variables and checks if they are equal or not action! Script 's directory on a Linux system, the filenames are in xyz.abc.d.CSV format a substring one! Improve this answer | follow | then the wildcards around the condition are wrong are xyz.abc.d.CSV! Wildcards around the bash check if string is in filename brackets I want to search for a particular text string and print the is. = operator use … bash check if two string are equal, or check the page. Expression matching when the right results Suggestions file using – cat filename … if string...: basename /path/to/file suffix furthermore, the filenames are in xyz.abc.d.CSV format need. Include the filename suffix is anything after the first argument value is read by original. Cover them all show you how to make an if statement to check whether the string length bash! Tutorials and FLOSS technologies used in combination with bash check if string is in filename operating system with it the pathname of following. Only read and execute commands from a file is not readable if -z: check if strings. Is long also have the same sequence of characters and other shells statement used! Use! = to check if a specified file exists bash will complain about..