Archive for the ‘computers’ Category
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
-
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
-
Substitute every occurence of foo with spam:
sed -e 's/foo/spam/g' test.txt
-
Substitute every occurence of foo with spam in the first two lines:
sed -e '1,2s/foo/spam/g' test.txt
-
Substitute every occurence of foo with spam in every line that starts with sausage and ends with egg:
sed -e '/^sausage.*egg$/s/foo/spam/g' test.txt
-
Substitute paths:
sed -e 's|/usr/bin/|/usr/local/bin|g' script.sh
-
Remove html tags:
<html> <body> Hello World! </body> </html>
sed -e 's/<[^>]*>//g' hello.html
Advanced substitution
-
Append (that’s what she said) to every line ( & represents what matches):
sed -e "s/^.*$/& (that's what she said)/g" test.txt
-
Append lol, rofl and lmao to the first three words of every line:
sed -e 's/\(^[^ ]*\) \([^ ]*\) \([^ ]*\)/\1lol \2rofl \3lmao/' test.txt
Multiple Commands
-
Print a file alternating row numbers:
sed -n -e '=;p' test.txt
-
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
-
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
-
Delete the first line of a file:
sed -e '1d' /etc/fstab
-
Delete from the second to the tenth line:
sed -e '2,10d' /etc/fstab
-
Delete lines starting with #:
sed -e '/^#/d' /etc/fstab
-
Print lines starting with #:
sed -n -e '/^#/p' /etc/fstab
-
Print blocks of text enclosed by BEGIN and END:
sed -n -e '/BEGIN/,/END/p' script.awk
-
Print Device section in xorg.conf:
sed -n -e '/Section "Device"/,/EndSection/p' /etc/X11/xorg.conf
-
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 
Godwin’s law
From Wikipedia:
“As a Usenet discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1.”
iNaz, the resource for human resources…
Talk about Apple and nazism
Awk by examples
AWK is a language for processing files of text. A file is treated as a sequence of records, and by default each line is a record. Each line is broken up into a sequence of fields, so we can think of the first word in a line as the first field, the second word as the second field, and so on. An AWK program is of a sequence of pattern-action statements. AWK reads the input a line at a time. A line is scanned for each pattern in the program, and for each pattern that matches, the associated action is executed.
Basics
-
Print /etc/mtab (awk reads a line at time and prints it) :
awk '{ print }' /etc/mtab
-
Print /etc/mtab ($0 denotes the whole line) :
awk '{ print $0 }' /etc/mtab
-
List mounted filesystems ($1 denotes the first element of the line) :
awk '{ print $1 }' /etc/mtab
-
List groups (-F chooses the Field Separator) :
awk -F":" '{ print $1 }' /etc/group
-
List groups and id (awk concatenates print() arguments) :
awk -F":" '{ print $1 " " $3 }' /etc/group
-
List groups and id (Nicer format) :
awk -F":" '{ print "group: " $1 "\tid: " $3 }' /etc/group
-
Launching external awk scripts :
# first.awk BEGIN { FS=":" } { print $1 }
awk -f first.awk /etc/mtab
-
List IPv4 addressess :
ifconfig | awk '/inet / { print $2 }'
-
List processes run by root :
# psroot.awk $1 == "root" { printf("ROOT: "); for (i=11; i<=NF; i++) printf("%s ", $i); printf("\n") }
ps au | awk -f psroot.awk
-
Print X warnings :
awk '$1 ~ /(WW)/ { print }' /var/log/Xorg.0.log
-
Print a file removing comments :
awk '! /^#/ { print }' /etc/fstab
-
Print number of files/directories :
ls -lA | awk 'BEGIN{ x=0 } { x=x+1 } END{ print x-1 }'
-
Awk as calculator :
echo | awk '{ print ((2*5^2-1)%7) }'
-
Count empty lines :
# blanklines.awk BEGIN { x=0 } /^$/ { x=x+1 } END { print "I found " x " blank lines :)" }
awk -f blanklines.awk /etc/profile
-
Use regexp as FS (note the difference though) :
echo ' a b c d '| awk -F"[ \t\n]+" '{ print $2 }'
echo ' a b c d '| awk -F" " '{ print $2 }'
-
Understand NR and NF :
# nrnf.awk BEGIN { x=0 } { print "Words on line " NR ": " NF ; x+=NF } END { print "Total lines: " NR ; print "Total words: " x }
awk -f nrnf.awk nrnf.awk