Archive for June, 2009
Sed by examples, Part 2
sed (stream editor) is a Unix utility which (a) parses text files and (b) implements a programming language which can apply textual transformations to such files.
It reads input files line by line (sequentially), applying the operation which has been specified via the command line (or a sed script), and then outputs the line.
Substitution
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Substitute, for every line, the first occurence of foo (if any) with spam:
# test.txt foo bar spam foo spam foo bar egg sausage foo spam egg spam spam spamsed -e 's/foo/spam/' test.txt
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Substitute every occurence of foo with spam:
sed -e 's/foo/spam/g' test.txt
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Substitute every occurence of foo with spam in the first two lines:
sed -e '1,2s/foo/spam/g' test.txt
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Substitute every occurence of foo with spam in every line that starts with sausage and ends with egg:
sed -e '/^sausage.*egg$/s/foo/spam/g' test.txt
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Substitute paths:
sed -e 's|/usr/bin/|/usr/local/bin|g' script.sh
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Remove html tags:
<html> <body> Hello World! </body> </html>
sed -e 's/<[^>]*>//g' hello.html
Advanced substitution
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Append (that’s what she said) to every line ( & represents what matches):
sed -e "s/^.*$/& (that's what she said)/g" test.txt
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Append lol, rofl and lmao to the first three words of every line:
sed -e 's/\(^[^ ]*\) \([^ ]*\) \([^ ]*\)/\1lol \2rofl \3lmao/' test.txt
Multiple Commands
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Print a file alternating row numbers:
sed -n -e '=;p' test.txt
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Print some information about your cpu first core:
# script.sed 1,/^$/{ /model name/p /flags/p /bogomips/p }
sed -n -f script.sed /proc/cpuinfo
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Add a line before/after each line or replace line:
# script.sed i\ This line will be inserted before each line# script.sed a\ This line will be inserted after each line# script.sed c\ This line will be inserted in each line
sed -f script.sed test.txt
Sed by examples
sed (stream editor) is a Unix utility which (a) parses text files and (b) implements a programming language which can apply textual transformations to such files.
It reads input files line by line (sequentially), applying the operation which has been specified via the command line (or a sed script), and then outputs the line.
Delete
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Delete the first line of a file:
sed -e '1d' /etc/fstab
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Delete from the second to the tenth line:
sed -e '2,10d' /etc/fstab
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Delete lines starting with #:
sed -e '/^#/d' /etc/fstab
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Print lines starting with #:
sed -n -e '/^#/p' /etc/fstab
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Print blocks of text enclosed by BEGIN and END:
sed -n -e '/BEGIN/,/END/p' script.awk
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Print Device section in xorg.conf:
sed -n -e '/Section "Device"/,/EndSection/p' /etc/X11/xorg.conf
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Print main function in a C source file:
sed -n -e '/main[[:space:]]*(/,/^}/p' source.c
How to colorize bash prompt easily
Sometimes, the bash prompt can look a little dull and it may become difficult to recognize where the output of a command ends. Here I provide with a very simple way to customize your bash prompt by adding some colors.
First of all, add these colors definition to your .bashrc
## Fancy colors red='\[\e[0;31m\]' RED='\[\e[1;31m\]' blue='\[\e[0;34m\]' BLUE='\[\e[1;34m\]' cyan='\[\e[0;36m\]' CYAN='\[\e[1;36m\]' black='\[\e[0;30m\]' BLACK='\[\e[1;30m\]' green='\[\e[0;32m\]' GREEN='\[\e[1;32m\]' yellow='\[\e[0;33m\]' YELLOW='\[\e[1;33m\]' magenta='\[\e[0;35m\]' MAGENTA='\[\e[1;35m\]' white='\[\e[0;37m\]' WHITE='\[\e[1;37m\]' NC='\[\e[0m\]' # No Color
The variables you want to use are
- \u – username
- \h – host name
- \w – current absolute path
- \W for current relative path
- \$ – te prompt character (eg. ‘#’)
For example, my current setup looks like:
PS1="${green}\u${NC}@${green}\h ${BLUE}\w${NC} ${GREEN}\$ ${NC} "
Enjoy 
Pearls Before Breakfast
Or “How we have become insensible to beauty”
Flood
A lawyer and an engineer were fishing in the Caribbean. The lawyer said, “I’m here because my house burned down, and everything I owned was destroyed by the fire. The insurance company paid for everything.”
That’s quite a coincidence,” said the engineer. “I’m here because my house and all my belongings were destroyed by a flood, and my insurance company also paid for everything.”
The lawyer thought for a moment, but was puzzled. Finally he asked the engineer, “How do you start a flood?”