Shell

Shell Scripting

^ OVERVIEW

This local page for Bash shell scripts and notes on shell scripting.

^ Bash Built-in Variables

Some links to useful articles discussing `bash` built-in variables:

• https://avpres.net/Bash/builtin_shell_variables
• https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html

Bash's built-in variables with short names, as listed in Kernigan and Ritchie's "Unix Programming" book and at the first linked article above:

$0
    The first element passed to the shell is the command name.
$n
    The nth argument passed on the command line. If n ≥ 10, then the syntax must be ${n}.
$*
    All the arguments on the command line. The values are separated by the first character in the shell variable IFS: (${1} … ${n}). See also: the IFS entry in Other Shell Variables.
$@
    All the arguments on the command line. The values are individually quoted: ("${1}" … "${n}").
$#
    The number of command-line arguments.
$?
    The exit value of the last executed command.
$_
    The last argument of the previous command.
$!
    The process ID of the most recent background process.

^ Rename Badly Named Files

How to produce a usable filename which contains <ESC> characters, and to rename that badly named file:

 $ ls -i
 9704871 $'\033\033'   9703029  CMakeLists.txt  10899590  dts          9708845  samples
 $ ls -q `find . -inum 9704871`
 './'$'\033\033'
 $ mv './'$'\033\033' betterfilename

^ Git Diff-tree Helper Script

A helper script for calling `git diff-tree`, which can be used to determine at which project commit one or more files have changed:

#!/bin/bash

# TODO: [ ] add first line of commit message above each set of file changes
# TODO: [ ] add command line option to accept count of commits to compare each neighbor to next commit

CMD_GIT=/usr/bin/git

$CMD_GIT log --oneline | head | cut -d " " -f 1

echo "2024-01-31 git diff-tree helper script in progress . . ."

hashes=`$CMD_GIT log --oneline | head | cut -d " " -f 1`
echo "In $PWD found git commit hashes:"
echo " " $hashes

#i=1
#for hash in $hashes; do echo "("$i")" $hash; (( i++ )); done

#echo "Files changed between commit pairs youngest pairings to oldest:
for hash in $hashes; do echo "Files changed in git commit:"; git diff-tree -r $hash; echo; done

echo "done"

exit 0