/ʃɛl/
noun … “the original Unix command interpreter for executing scripts and commands.”
sh, short for the Bourne shell, is a Unix command-line interpreter and scripting language created by Stephen Bourne in 1977. It provides a standard interface for users and scripts to interact with the operating system, execute commands, control processes, and manipulate files. As one of the earliest shells, sh established foundational syntax and constructs that influenced nearly all subsequent Unix shells, including Bash, ksh, and zsh.
The functionality of sh includes command execution, pipelines, I/O redirection, variables, loops, conditionals, and functions. Scripts written in sh allow for automation of repetitive tasks, configuration of environments, and orchestration of system operations. Its design emphasizes simplicity, portability, and adherence to POSIX standards, ensuring scripts can run across different Unix-like systems without modification.
sh interacts naturally with other command-line utilities. For instance, commands like grep, sed, and awk are often used in sh scripts to process text, filter data, and perform transformations. It also provides the foundation for more advanced shells such as Bash, which extend sh with features like job control, command-line editing, arrays, and improved scripting constructs.
In practice, sh is used for boot scripts, system initialization, automation of administrative tasks, and portable shell scripts distributed across diverse Unix-like environments. Its minimalistic syntax and wide adoption make it a reliable tool for both interactive use and scripted automation.
An example of an sh script:
#!/bin/sh
# Print disk usage of home directories
for dir in /home/*; do
echo "$dir: $(du -sh $dir)"
done
The intuition anchor is that sh acts as the “original command translator” for Unix: it interprets user instructions, sequences commands, and automates operations, laying the groundwork for all modern Unix shells and scripting environments.