Basic but Very important Linux Commands.

 Unix text tools

There are few standard text processing tools which are used very often on the Unix-like system.

• No regular expression is used:
  
  • cat(1) concatenates files and outputs the whole content.
  • tac(1) concatenates files and outputs in reverse.
  • cut(1) selects parts of lines and outputs.
  • head(1) outputs the first part of files.
  • tail(1) outputs the last part of files.
  • sort(1) sorts lines of text files.
  • uniq(1) removes duplicate lines from a sorted file.
  • tr(1) translates or deletes characters.
  • diff(1) compares files line by line.
• Basic regular expression (BRE) is used:
  
  • grep(1) matches text with patterns.
  • ed(1) is a primitive line editor.
  • sed(1) is a stream editor.
  • vim(1) is a screen editor.
  • emacs(1) is a screen editor. (somewhat extended BRE)
• Extended regular expression (ERE) is used:
  
  • egrep(1) matches text with patterns.
  • awk(1) does simple text processing.
  • tcl(3tcl) can do every conceivable text processing: re_syntax(3). Often used with tk(3tk).
  • perl(1) can do every conceivable text processing. perlre(1).
  • pcregrep(1) from the pcregrep package matches text with Perl Compatible Regular Expressions (PCRE) pattern.
  • python(1) with the re module can do every conceivable text processing. See "/usr/share/doc/python/html/index.html".

  
  

  Recording the shell activities cleanly

  The simple use of script(1) (see Section 1.4.9, “Recording the shell activities”) to record shell activity produces a file with control characters. This can be avoided by using col(1) as the following.
  

  $ script
  Script started, file is typescript

  Do whatever … and press Ctrl-D to exit script.
  

  $ col -bx <typescript >cleanedfile
  $ vim cleanedfile

  If you don't have script (for example, during the boot process in the initramfs), you can use following instead.
  

  $ sh -i 2>&1 | tee typescript