Examples #. [ -e FILE] True if FILE exists. (*.txt) to match all names not ending with .txt), it enables glob patterns to match hidden names, and it makes the pattern expand to nothing at all if nothing matches. ; pidof command – Find the process ID of a running program on Linux or Unix-like system; ps command – Get information about the currently running Linux or Unix processes, including … [ -d FILE] True if FILE exists and is a directory. But sometimes it does not, so the next shell prompt is printed in the same line together with the output. When used in shell scripts, the value supplied as an argument to the exit command is returned to the shell as an exit code.. Line 8 - fi signals the end of the if statement. [ -b FILE] True if FILE exists and is a block-special file. Usually though in a bash script you want to check if the argument is empty rather than if it is not empty, to do this you can use the -z operator. For example: Primary Meaning [ -a FILE] True if FILE exists. If that is a fair assessment, then I would recommend testing the string to see if it does refer to a directory or not. The echo statement prints its argument, in this case, the value of the variable count, to the terminal window. You can compare number and string in a bash script and have a conditional if loop based on it. if [ -z $1 ] then echo "sorry you didn't give me a value" exit 2 fi If value is not true. [ -f FILE] True if FILE exists and is a regular file. Bash check if process is running or not. [ -g FILE] True if FILE exists and its SGID bit is set. @Hatclock No, not at all. Line 6 - The backslash ( \ ) in front of the single quote ( ' ) is needed as the single quote has a special meaning for bash and we don't want that special meaning. End every if statement with the fi statement. The only impact of exit 0 at the end of the script is to return 0 instead of the status from the previous instruction. In programming, conditions are crucial : they are used to assert whether some conditions are true or not.. The -z operator is the opposite of -n, you could get the same results by performing this if statement with the ! [ -c FILE] True if FILE exists and is a character-special file. All commands after this will be run as normal. If offset evaluates to a number less than zero, the value is used as an offset from the end of the value of parameter. If parameter is @, the result is length positional parameters beginning at offset. Okay, save your bash script, give permission with … If N is not given, the exit status code is that of the last executed command.. Bash commands to check running process: pgrep command – Looks through the currently running bash processes on Linux and lists the process IDs (PID) on screen. Most of the time the output of a command ends with the newline character. Numeric and String Comparison. When working with Bash and shell scripting, you might need to use conditions in your script.. else –» and this is the other “flag” that tells bash that if the statement above was not true (false), then execute the command here instead. The backslash escapes the special meaning to make it a normal plain single quote again. Example: root@hostname [~] # echo -n hello helloroot@hostname [~] # I've always found that very annoying. The bash scripting language uses this convention to mark the end of a complex expression, such as an if statement or case statement. – Gilles 'SO- stop being evil' Sep 6 '16 at 22:08 Of course, you may wish to do more detailed testing. The following example sets a variable and tests the value of the variable using the if statement. echo 'odd' –» it prints “odd” to your screen fi –» end of the if statement. The fact that a string ends in a slash does not mean that the string refers to a directory. 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