Shell Scripting

Shell scripting refers to writing scripts for command-line interpreters (shells) such as Bash, Zsh, or Sh. Shell scripts automate tasks, manage system operations, and streamline workflows in Unix-like environments.

Shell scripting is valued for:

Automation: Enables repetitive tasks to be automated, saving time and reducing errors.
Portability: Scripts can often run on any Unix-like system with minimal changes.
Integration: Easily integrates with other command-line tools and utilities.
Text Processing: Powerful for manipulating and processing text files using tools like awk, sed, and grep.
System Administration: Widely used for managing users, processes, backups, and deployments.
Rapid Prototyping: Quick to write and modify for testing ideas or workflows.
Community Support: Extensive documentation and a large community provide abundant resources and examples.

Shell scripting continues to be a fundamental skill for developers, system administrators, and DevOps engineers, evolving with new shells and features.

Web Site

Tools

Bash
Zsh
Sh
Fish
ShellCheck
awk
sed
grep

Basic

Handle date format in shell

date +"%Y_%m_%d_%H_%M"
# -----
#   2026_03_12_04_10

Specifier	Description	Example
%a	locale’s abbreviated weekday name (e.g., Sun)	Sun
%A	locale’s full weekday name (e.g., Sunday)	Sunday
%b	locale’s abbreviated month name (e.g., Jan)	Jan
%B	locale’s full month name (e.g., January)	January
%c	locale’s date and time (e.g., Thu Mar 3 23:05:25 2005)
%C	century; like %Y, except omit last two digits (e.g., 20)
%d	day of month (e.g., 01)	01
%D	date; same as %m/%d/%y
%e	day of month, space padded; same as %_d
%F	full date; same as %Y-%m-%d
%g	last two digits of year of ISO week number (see %G)
%G	year of ISO week number (see %V); normally useful only with %V
%h	same as %b
%H	hour (00..23)
%I	hour (01..12)
%j	day of year (001..366)
%k	hour, space padded ( 0..23); same as %_H
%l	hour, space padded ( 1..12); same as %_I
%m	month (01..12)
%M	minute (00..59)
%n	a newline
%N	nanoseconds (000000000..999999999)
%p	locale’s equivalent of either AM or PM; blank if not known
%P	like %p, but lower case
%r	locale’s 12-hour clock time (e.g., 11:11:04 PM)
%R	24-hour hour and minute; same as %H:%M
%s	seconds since 1970-01-01 00:00:00 UTC
%S	second (00..60)
%t	a tab
%T	time; same as %H:%M:%S
%u	day of week (1..7); 1 is Monday
%U	week number of year, with Sunday as first day of week (00..53)
%V	ISO week number, with Monday as first day of week (01..53)
%w	day of week (0..6); 0 is Sunday
%W	week number of year, with Monday as first day of week (00..53)
%x	locale’s date representation (e.g., 12/31/99)
%X	locale’s time representation (e.g., 23:13:48)
%y	last two digits of year (00..99)
%Y	year
%z	+hhmm numeric time zone (e.g., -0400)
%:z	+hh:mm numeric time zone (e.g., -04:00)
%::z	+hh:mm:ss numeric time zone (e.g., -04:00:00)
%:::z	numeric time zone with : to necessary precision (e.g., -04, +05:30)
%Z	alphabetic time zone abbreviation (e.g., EDT)

Substring To slice a variable or string is to substring, we could use the cut command.

val="some value"
echo "echo $val | cut -c1-6"
# output:
# some v

Shell Script basic initializer

Script that change directory to the script location
Return to the origina directory when done (trap can do finally operation)

CUR_DIR="$( cd -P "$( dirname "$1" )" >/dev/null 2>&1 && pwd )"
SCRIPT_DIR="$( cd -P "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
pushd $SCRIPT_DIR > /dev/null
echo "Switch current directory: $(pwd)" >&2
cleanup() {
    popd > /dev/null
    echo "Current directory after popd: $(pwd)" >&2
}
trap cleanup EXIT

# your script below

Shell Scripting

Web Site

Tools

Basic

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