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There are many Linux/Unix shells (bash, tcsh/csh, ksh, zsh...), but bash has become the most popular, probably because it is the default shell in open-source Linux.
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- a command-line interpreter (a.k.a. Read-Eval-Print loop, or REPL)
- a rich set of built-in commands for file system navigation & data manipulation
- advanced utility programs (e.g. cut, join, paste, sort, grep, sed, awk, perl)
- some of which are full-featured programming languages of their own (awk, perl)
- many programming language features
- variables, variable types, control structures, functions
- a lot of weird but powerful syntax (piping, redirection)
- a highly extensible execution environment
- enables calling of both built-in and custom scripts & programs
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The combination of piping, a large set of built-in utilities, and the ease of creating and troubleshooting long "command line one-liners" provides tremendous productivity potential over, for example, having to write a Python program to achieve equivalent results.
This Cut, sort, uniq and piping a histogram discussion in the Intermediate Unix course provides a good example.
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