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Bash substring extractions

(2021/07/27)

Bash allows for easy (and pretty powerful) substring extractions.

Syntax:

${<SOURCE_STRING><OPERATOR><MATCHING_PATTERN>}

MATCHING_PATTERN:

Follows the usual pattern matching techniques.

E.g. *ski matches "Bartek Lipinski".

OPERATOR:

  • # deletes the shortest match of MATCHING_PATTERN searching from the front of SOURCE_STRING.

    URL='https://www.youtube.com/watch?v=dQw4w9WgXcQ'
SUBSTRING="${URL#*://}"
# SUBSTRING is 'www.youtube.com/watch?v=dQw4w9WgXcQ'

# removes the shortest string that matches `*://` from the front of $URL

  • ## deletes the longest match of MATCHING_PATTERN searching from the front of SOURCE_STRING.

    URL='https://www.youtube.com/watch?v=dQw4w9WgXcQ'
SUBSTRING="${URL##*/w}"
# SUBSTRING is 'atch?v=dQw4w9WgXcQ'

# removes the longest string that matches `*/w` from the front of $URL
# if it was using '# (the shortest) the SUBSTRING would be 'ww.youtube.com/watch?v=dQw4w9WgXcQ'
# but for the '##' SUBSTRING is 'atch?v=dQw4w9WgXcQ' because it matches the last '/w'

  • % deletes the shortest match of MATCHING_PATTERN searching from the end of SOURCE_STRING.

  • %% deletes the longest match of MATCHING_PATTERN searching from the end of SOURCE_STRING.