Manipulating Strings

String Length

${#string}

expr length $string

    These are the equivalent of strlen() in C.
expr "$string" : '.*'

Length of Matching Substring at Beginning of String

expr match "$string" '$substring'

    $substring is a regular expression.
expr "$string" : '$substring'

    $substring is a regular expression.

Index

expr index $string $substring

    Numerical position in $string of first character in $substring that matches.

Substring Extraction

${string:position}

    Extracts substring from $string at $position.

    If the $string parameter is "*" or "@", then this extracts the positional parameters, [1] starting at $position.
${string:position:length}

    Extracts $length characters of substring from $string at $position.

expr substr $string $position $length

    Extracts $length characters from $string starting at $position.

expr match "$string" '\($substring\)'

    Extracts $substring at beginning of $string, where $substring is a regular expression.
expr "$string" : '\($substring\)'

    Extracts $substring at beginning of $string, where $substring is a regular expression.

expr match "$string" '.*\($substring\)'

    Extracts $substring at end of $string, where $substring is a regular expression.
expr "$string" : '.*\($substring\)'

    Extracts $substring at end of $string, where $substring is a regular expression.

Substring Removal

${string#substring}

    Deletes shortest match of $substring from front of $string.
${string##substring}

    Deletes longest match of $substring from front of $string.

${string%substring}

    Deletes shortest match of $substring from back of $string.

${string%%substring}

    Deletes longest match of $substring from back of $string.

Substring Replacement

${string/substring/replacement}

    Replace first match of $substring with $replacement. [2]
${string//substring/replacement}

    Replace all matches of $substring with $replacement.

${string/#substring/replacement}

    If $substring matches front end of $string, substitute $replacement for $substring.
${string/%substring/replacement}

    If $substring matches back end of $string, substitute $replacement for $substring.