Download Advanced Bash-Scripting Guide by Mendel Cooper PDF

By Mendel Cooper

This can be the entire reference at the Borne back shell (bash). quantity 1Volume 2 comprises all appendices.

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Sh 1 2 3 4 5 4 # However, as Eleni Fragkiadaki, points out, #+ attempting a 'shift' past the number of #+ positional parameters ($#) returns an exit status of 1, #+ and the positional parameters themselves do not change. # This means possibly getting stuck in an endless loop. . # For example: # until [ -z "$1" ] # do # echo -n "$1 " # shift 20 # If less than 20 pos params, # done #+ then loop never ends! # # When in doubt, add a sanity check. . # shift 20 || break # ^^^^^^^^ The shift command works in a similar fashion on parameters passed to a function.

0 ! true echo "exit status of \"! " needs a space between it and the command. ' operator prefixing a command invokes the Bash history mechanism. true # No error this time, but no negation either. # It just repeats the previous command (true). # Thanks, Stéphane Chazelas and Kristopher Newsome. Certain exit status codes have reserved meanings and should not be user-specified in a script. Chapter 6. Exit and Exit Status 47 Chapter 7. Tests Every reasonably complete programming language can test for a condition, then act according to the result of the test.

The shift command can take a numerical parameter indicating how many positions to shift. sh shift 3 # Shift 3 positions. # n=3; shift $n # Has the same effect. sh 1 2 3 4 5 4 # However, as Eleni Fragkiadaki, points out, #+ attempting a 'shift' past the number of #+ positional parameters ($#) returns an exit status of 1, #+ and the positional parameters themselves do not change. # This means possibly getting stuck in an endless loop. . # For example: # until [ -z "$1" ] # do # echo -n "$1 " # shift 20 # If less than 20 pos params, # done #+ then loop never ends!

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