Bash cheatsheet

Useful commands

• dirname [file] : get path of a file
• pushd [directory] : push cwd to stack, set cwd to directory
• popd : pop stack to cwd
• exit [status] : terminate a script
• set -e : terminate script if any cmds exits with error
• A || B : exec B only if A fails

Variables

• VAR=VALUE : set variable
• ${VAR} : get variable
• $VAR : get variable
• VAR=$(CMD) : store result of cmd exec in variable

Special variables

• $0 : first arg of script = name of script
• $@ : cmd args of script
• $# : num of args
• $? : exit status of last command executed
• ${BASH_SOURCE} : filename+path of the current script being executed
• #!/bin/bash : Specifies which shell should be used to execute the script

Conditions

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if [ ... ]; then
    # something
elif [ ... ]; then
    # something else
else
    # something else
fi

Conditional expressions

Always enclose variable with " "!

• VAR == "debug" : == string
• "$VAR" != "string" : != string
• -eq 0 : == value
• ! -eq 0 : != value
• -gt 0 : > value
• -v VAR : variable is set/exists
• -z VAR : variable is unset/empty
• -n "$VAR" : string in variable is empty
• -f "file.txt" : file exists