cheat sheets.

Cheat Sheet Title: [ no_spaces_alphanumeric_only ]

Cheat Sheet:
Bash parameter expansions ========================= NOTE: The `:' character used in many of the expansions is optional. Using the `:' checks for param that is unset or null. Without the `:' checks for param that is unset. | Expansion | Note | |--------------------------+---------------------------------| | ${param} | Use value | | ${!param} | Variable indirection | | ${param:-word} | Use default value | | ${param:=word} | Assign default value | | ${param:?word} | Display error | | ${param:+word} | Use alternate value | | ${param:offset} | Substring expansion | | ${param:offset:length} | Substring expansion with length | | ${!prefix*} | Name expansion with prefix | | ${#param} | Length in characters | | ${param#word} | Remove shortest match at start | | ${param##word} | Remove longest match at start | | ${param%word} | Remove shortest match at end | | ${param%%word} | Remove longest match at end | | ${param/pattern/string} | Replace first matching pattern | | ${param//pattern/string} | Replace all matching patterns | Examples: $ x=yes $ echo ${x} #=> yes $ echo ${x:-no} #=> yes $ x= $ echo ${x:-no} #=> no $ echo ${x-no} #=> "" <an empty string> $ unset x $ echo ${x:-no} #=> no $ echo ${x-no} #=> no $ path='/some/path/to/file.txt' $ echo ${path##*/} #=> file.txt $ echo ${path%/*} #=> /some/path/to $ x=yes $ y=x $ echo ${!y} #=> yes $ x=0123456789 $ echo ${x:0} #=> 0123456789 $ echo ${x:3} #=> 3456789 $ echo ${x:3:2} #=> 34 $ xval1=first $ xval2=second $ xval3=third $ echo ${!xval*} #=> xval1 xval2 xval3

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