insert text after one line which contains patterns

In a file I would like to insert a line after the line which contains "MRINI".

1) firstly, find the line number which contains the pattern
 set line_number =  `sed  -n  '/MRINI/='   filename `

-n : to only print the line number, not print the pattern space

2) use sed to insert a line after the line_number. The line to insert is:

    1 7840    0    0    0    0    0    0               fin correction mesures

The command is:   sed -e "${line_number}a \line_to_insert"   filename

sed   -e   "${line_number}a\    1 7840    0    0    0    0    0    0               fin correction mesures"       filename   > new_filename

Note: 

i) the double quote is used in 2) since the variable ${line_number} is used in the command.

ii) In the command sed -e "${line_number}a \line_to_insert"   filename ,

a\line_to_insert represents that we append the line_to_insert 

If use i\line_to_insert: insert the line_to_insert in the $line_number, ie., before the line which contains the pattern MRINI

iii) in 1) we use   '/MRINI/='  

= represents that we print the current line number where it contains the pattern MRINI

add characters in the beginning/end of each line

---- add "\hline" in the begining of each line in a file one_year_stat
sed 's/^/ \\hline /' one_year_stat  > tt

---- add "\" in the end of each line in a file:
sed 's/$/ \\/'    tt 

---- add " &" in the end of each line in a file:

sed 's/$/  \&/'   tt

---- replace the last occurence of & in each line of a file with a space:

sed 's /\(.*\)& /\1 /' one_year_stat

-----If the new text contains "/", eg a path /home/user/tt, then the sed 's/../g' does not work. We should use "|" instead of "/"
set aa = /home/user/tt
sed   "s|^|${aa}|g"    txt_file 


NOTE: For special characters such as \ or &;, if we want to add then in the text file using the sed. We need put \ before them such that they may be added in the file.

sed to replace a string in a file and save it

#!/bin/bash

for i in $(ls -d p*); do
    echo $i
    cd $i
    echo $PWD
    grep "elseif (( hrut .gt. 29.2)" *
    sed -i 's/(( hrut .gt. 29.2) then/( hrut .gt. 29.2) then/g'  file.f;   
   cd ..

done

sed -i  's/string1/string2/g'  file:
it can replace the string1 with string 2 in the file, and save the modified file with the original name.


____ to replace strings at certain lines:
set a = 50
set b = 60
sed -e "$a,${b}s/string1/string2/g"  file

This is to replace the string1 with string2 at lines between 50 and 60 in a file

sed: remove text between two keywords

If the inputfile contains:

la1_22000
la1_22066
la1_22124
la1_22236
la1_22341
la1_22431
la1_22572

In order to remove the text between two lines which contains the keywords la1_22066 and la1_22431 respectively,

set keyword1 = la1_22066
set keyword2 = la1_22431
sed "s/$keyword1/,/$keyword2/d"    inputfile


Attention: in order to use variables in SED, it is better to use double quote than single quote.


If we have special characters in the keyword, for example, /, what we can do is to add \ before it, such that the system can identify this special character.

Example: to repalce /aaa with /bbb
set 's/\/aaa/\/bbb/g' inputfile

get text of between specific lines using sed

1) sed -n 'linenumber1,linenumber2p'  file
sed -n '10, 20p' file

Print all the lines between 10 and 20 of a file

Similarly, if you want to print from 10 to the end of line you can use: sed -n '10,$p' filename

This is especially useful if you are dealing with a large file. Sometimes you just want to extract a sample without opening the entire file.

If use variables to define the line number, then we need use double quote and {}:
set a = 1
set b = 5
sed -n "$a, ${b}p" stations_igs_final

2) sed -n 5p  file

To print a specific line (line 5) from a file

or use awk:

cat file | awk -v n=5 '{if (NR==n)print $0}'

find and change in text with grep and sed

given a text file ($file) containing:


1.0  1  user  /home/user/tahiti_la2_mrb0/la2_22530_elim_1fois
1.0  1  user  /home/user/tahiti_la2_mrb0/la2_22540_elim_1fois
1.0  1  user  /home/user/tahiti_sta_mrb0/sta_22460_elim_1fois
1.0  1  user  /home/user/tahiti_sta_mrb0/sta_22470_elim_1fois


if we want to change the 1.0 to 0.6 in any line which contains "la", and change 1.0 to 1.2 in any line which contains "st", we can do:


cat  $file  |  grep "_la"   | sed   's/1./0.6/'     >> $file"_0.61.2"
cat  $file  |  grep "_st"   | sed   's/1./1.2/'     >> $file"_0.61.2"

sed regular expression

^	matches the beginning of the line
$	matches the end of the line
.	Matches any single character
(character)*	match arbitrarily many occurences of (character)
(character)?	Match 0 or 1 instance of (character)
[abcdef]	Match any character enclosed in [] (in this instance, a b c d e or f) ranges of characters such as [a-z] are permitted. The behaviour of this deserves more description. See the page on grep for more details about the syntax of lists.
[^abcdef]	Match any character NOT enclosed in [] (in this instance, any character other than a b c d e or f)
(character)\{m,n\}	Match m-n repetitions of (character)
(character)\{m,\}	Match m or more repetitions of (character)
(character)\{,n\}	Match n or less (possibly 0) repetitions of (character)
(character)\{n\}	Match exactly n repetitions of (character)
\(expression\)	Group operator.
\n	Backreference - matches nth group
expression1\|expression2	Matches expression1 or expression 2. Works with GNU sed, but this feature might not work with other forms of sed.

A very useful link about sed is:

 http://www.ibm.com/developerworks/linux/library/l-sed2/index.html

add in the end of line, sed

1) in sed, "^" represents the begining of a line, and "$" the end of line, "^$" a blank line

2) if we want to add a string in the end of each line of a text file and save it to a new file:


#!/bin/csh
# find each file starting with "input" and apply the changes
foreach i ( `ls input*` )
    # get the last string in the filename separated by _
    set append = `echo $i | awk '{split($0,a, "_");print a[6]}' `     


    # add _elim_1fois at the end of each line and save it to a new file
    sed    's/$/_elim_1fois/'   $i  >> $i"_elim_1fois_"$append 
   
    sed   's/$/_elim_2fois/'    $i  >> $i"_elim_2fois_"$append


end

replace a line in a text file with sed

I have a text file which defines the values of some important variables. Such a text file is used for several simulations. I need to change the value of one parameter in the file:
ap = 24.1, to a smaller value 3.

what I do is to use the sed.
sed 's/to_be_replace/replaced_result/' text file

mv text_file tt
sed 's/ap = 24.1,/ap = 3,/p' tt > text_file

then the old text file is modified with the ap value !