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.

^ Getopt and Getopts

The shell page section to cover `getopt` and `getopts`, two libraries or facilities available to Bash shell scripts to process command line arguments.

An introduction to `getopt` at Labex dot io:

• https://labex.io/tutorials/shell-bash-getopt-391993

^ 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

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 . . ."
echo "got $# arguments, arg one single quoted is '$1'"

hashes=`$CMD_GIT log --oneline | head -n ${1} | 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
for hash in $hashes
    do echo "Files changed in git commit:"
    git log -1 --oneline $hash
    git diff-tree -r $hash
    echo
done

echo "done"

exit 0

Script to test compilation of series of git commits:

#!/bin/bash

CMD_GIT=/usr/bin/git

VETTED_COMMITS_FILE="branch-commit-vetting-report.txt"
current_branch="NOT_SET"
hashes="NOT_SET"

function usage()
{
    echo "How to use vet-branch.sh:":
    echo
    echo "  $ vet-branches.sh n"
    echo
    echo "Argument 'n' is a number of commits to test in current git branch."
    echo
}

#
# script starting point, akin to int main
#

echo "$0: starting"
if [ $# -lt 1 ] 
then
    echo "$0 called with too few arguments!"
    usage
    exit -1  
fi

current_branch=`$CMD_GIT branch --show-current`
hashes=`$CMD_GIT log --oneline | head -n $1 | cut -d " " -f 1`

echo "Vetting $1 commits of branch ${current_branch}."
echo "Asked to test commits: $hashes"
echo

date >> $VETTED_COMMITS_FILE
echo "Testing compilation of $1 commits start at tip of '$current_branch':" >> $VETTED_COMMITS_FILE

for hash in $hashes
    do  
    $CMD_GIT checkout --quiet $hash
    echo
    echo "At commit $hash, vetting script in progress"
    echo "---------------------------------------------"
    ./scripts/docker-helper.sh build_both_debug
    echo "$hash build result: $?" >> $VETTED_COMMITS_FILE
done

echo
echo "Restoring git checkout to starting branch:"
$CMD_GIT checkout $current_branch
echo "$0: done."

exit #?

^ Shell Logging Helper

Bash and related shell programming definitely have their limitations, with numeric and mathematical handling, name spaces and more. Despite these shortfalls we still want to debug shell programs. Noted here is an idea to collect some logging shell functions in a script which can be sourced by other shell scripts.

Code excerpt, not complete:

#!/bin/bash

# @brief Bash script fragment, collection of functions to aid with shell script
#  debugging.
#
# @note Script adopts the notion of log levels as implemented in Zephyr RTOS.
#   From most critical to most verbose these levels are:
#
#   Error, Warning, Info, Debug
#
#  ERR
#  WRN
#  INF
#  DBG

function set_script_log_level()
{

}

# @brief This function expects:
#
# $1 . . . message to print
# $2 . . . log level used to filter printing

function diag()
{

}

^ To Research

[ ] Look up `git ls-files` and its options.

[ ] Review `xargs` called with the dash zero option.

Interesting header file from Zephyr RTOS 3.4.0:

`zephyr/include/zephyr/toolchain/xcc_missing_defs.h`

Shell command substitution backticks versus braces . . .

• https://stackoverflow.com/questions/22709371/backticks-vs-braces-in-bash