shell

Filename

cmd

result

./t.sh

$(basename $0)

t.sh

$(basename $0 .sh)

${PWD##*/}

parent_dir_name

Pattern Matching

https://www.gnu.org/software/bash/manual/html_node/Pattern-Matching.html

Operations on variables

https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html#Shell-Parameter-Expansion

type

example

result

Length

echo ${#SHELL}

${parameter:-$var}

${NULL:-$SHELL}

/bin/bash

${parameter:-word}

echo ${SHELL:-ignored}

/bin/bash

[ -z "${COLUMNS:-}" ] && COLUMNS=80 ; echo $COLUMNS

${parameter:=word}

unset a ; echo ${a:=b} ; echo $a

b b

${VAR:OFFSET:KEEP}

echo ${SHELL:0:4}

/bin

${VAR/PATTERN/NEW}

echo ${SHELL/b/}

/in/bash

${VAR//PATTERN/NEW}

echo ${SHELL//b/}

/in/ash

${VAR#beginning}

echo ${SHELL#*/}

bin/bash

${VAR##beginning}

echo ${SHELL##*/}

bash

${VAR%trailing}

${SHELL%/*h}

/bin

heredoc

https://en.wikipedia.org/wiki/Here_document#Unix_shells

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