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More Commands

CS155 Commands3

sed – stream editor

• sed is a non-interactive editor that operates on streams.
• The most common usage is some form of:
  sed 's/pattern/replace/' file > new
• sed does not change the contents of the original file. Use > to send changed output to a new file.
• A nice introduction: http://www.grymoire.com/Unix/Sed.html

sed syntax

All lines:	sed 'command' filename
One line:	sed 'line command' filename
Range of lines:	sed 'startline,endline command' filename

Commands:

• s/old/new/ (with optional g flag)
• d
• Many others

sed line specification

A line specification in sed can be:

• A number
• $ - the last line
• /pattern/

sed: A Few Examples

• Replace all instances of hello with goodbye in new_file:
  sed 's/hello/goodbye/g' new_file
• Delete all lines that occur between foo and bar in file:
  sed '/foo/,/bar/d' file
• Delete all lines that contain the word “bob” in data:
  sed '/bob/d' data

sed: A Few Examples

• Delete lines 2–5 of new_file (but don't change new_file!):
  sed '2,5d' new_file
• Replace foo with bar in the first 5 lines of file:
  sed '1,5s/foo/bar/g' file

sed: More Examples

• Remove some punctuation characters:
  sed 's/[,.?-]//g' filename
• Strip blanks from beginning of lines:
  sed 's/^ *//' filename
• Strip blanks from end of lines:
  sed 's/ *$//' filename

A Little More Regular Expression Syntax

• In regular expressions, we escape characters by preceding them with a backslash.
• Escaping a character does one of two things:
  • removes the special meaning of special characters
  • gives special meaning to non-special characters
• Examples:
  • . matches any character, but \. matches only the dot itself.
  • ? matches itself, but \? is a special character

Alternation through Escaping

• \| can be used to match either of two patterns:
  grep 'one\|two' files

diff: Comparing Files

• Usage: diff file1 file2
• diff describes the modifications that should be applied to file1 to create file2

file1	file2
hello world. this is file1. it's a lame file. the end.	hello world. this is file2. it's a sweet file. the end. maybe not.

diff: Comparing Files

% diff file1 file2
2,3c2,3
< this is file1.
< it's a lame file.
--
> this is file2.
> it's a sweet file.
4a5
> maybe not.

• line1start, line1end action line2start, line2end
  • a – add
  • c – change
  • d – delete

file: Getting Information on File Type

• The file command attempts to determine the type of a file:

% file Honda.pdf
Honda.pdf: PDF document, version 1.4
% file AdobeFnt.lst
AdobeFnt.lst: PostScript document text
% file Xrootenv.0
Xrootenv.0: ASCII text, with very long lines
% file school/cs553.tgz
school/cs553.tgz: gzip compressed data, from Unix
% file /bin/bash
/bin/bash: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for GNU/Linux 2.2.5, dynamically linked (uses shared libs), for GNU/Linux 2.2.5, stripped