Wiki/bash.md

Bash

File handling

• Read from file: variable=$(<$filePath)
• Check if file (not directory or device) exists: if [[ -f $filePath ]]
• Check if file exists: if [[ -e $filePath ]]
• Check if directory exists: if [[ -d $filePath ]]
• Write to file echo "SomeString" > $filePath
• Get directory name "$(dirname $someFile)"

• Edit previous command !!.s/<mistakeInCommand>/<correctedCommand>

• Edit previous command ^<mistakeInCommand>^<correctedCommand>^

• Check if variable is unset -z/ set -n

• Iterate over files: for f in *; do echo "File: ${f}"; done

• Rename files somehow: for f in *_Something_*; do echo $(echo $f | cut -d '_' -f 1,2); done

• Replace first occurrence of pattern: ${myVar/myPattern/myString}

• Replace all occurrences of pattern: ${myVar//myPattern/myString}

• Remove leading a: temp="${opt%a}"

• Remove trailing a: temp="${opt#a}"

• Function output to variable: result=$(myfunc)

SSH

• Execute set of commands on remote

ssh MYREMOTE /bin/bash << EOF
    cmd1;
    cmd2;
    cmd3
EOF
if [ $? -ne 0 ]; then
    # One of the commands failes
fi

• Return code is return code of executed command

  • Except if ssh fails

• Combine command outputs: { command1 & command2; }

  • Can also be redirected: { command1 & command2; } > new_file