Shell Script Replace a Specified Column with sed

Question

I have a example dataset separated by semicolon as below;

123;IZMIR;ZMIR;123
abc;ANKAR;aaa;999
AAA;ZMIR;ZMIR;bob
BBB;ANKR;RRRR;ABC

I would like to replace values in a specified column. Lets say I want to change "ZMIR" AS "IZMIR" but only for the third column, the ones on the second column must stay the same.

Desired output is;

123;IZMIR;IZMIR;123
abc;ANKAR;aaa;999
AAA;ZMIR;IZMIR;bob
BBB;ANKR;RRRR;ABC

I tried;

sed 's/;ZMIR;/;IZMIR;/' file.txt

the problem is that it changes all the values on the file not just the 3rd one.

I also tried;

awk -F";" '{gsub("ZMIR",";IZMIR;",$2)}1'

and here it specifies the column but, it somehow adds spaces;

123 I;IZMIR; ZMIR 123
abc;ANKAR;aaa;999
AAA ;IZMIR; ZMIR bob
BBB;ANKR;RRRR;ABC

Answer 1

sed doesn't know about columns, awk does (but in awk they're called "fields"):

awk 'BEGIN{FS=OFS=";"} $3=="ZMIR"{$3="IZMIR"} 1' file

Note that since the above is doing a literal string search and replace, you don't have to worry about regexp or backreference metacharacters in the search or replacement strings, unlike in a sed solution (see https://stackoverflow.com/a/29626460/1745001).

wrt what you tried previously with awk:

awk -F";" '{gsub("ZMIR",";IZMIR;",$2)}1'

That says: find "ZMIR" in the 2nd semi-colon-separated field and replace it with ";IZMIR;" and also change every existing ";" on the line to a blank character.

To learn awk, read the book Effective Awk Programming, 4th Edition, by Arnold Robbins.

Answer 2

If you exactly know where the word to replace is located and how many of them are in that line you could use sed with something like:

sed '3 s/ZMIR/IZMIR/2'

With the 3 in the beginning you are selecting the third line and with the 2 in the end the second occurrence. However the awk solution is a better one. But just that you know how it works in sed ;)

Answer 3

This might work for you (GNU sed):

sed -r 's/[^;]+/\n&\n/3;s/\nZMIR\n/IZMIR/;s/\n//g' file

Surround the required field by unique markers then replace the required string (plus markers) by the replacement string. Finally remove the unique markers.

Answer 4

Perl on Command Line

Input

123;IZMIR;ZMIR;123  
000;ANKAR;aaa;999  
AAA;ZMIR;ZMIR;bob  
BBB;ANKR;RRRR;ABC    

$. == 1 means first row it does the work only for this row So second row $. == 2
$F[0] means first column and it only does on this column So fourth column $F[3]
-a -F\; means that delimiter is ;

what you want
perl -a -F\; -pe 's/$F[0]/***/ if $. == 1' your-file

output

***;IZMIR;ZMIR;123  
abc;ANKAR;aaa;999  
AAA;ZMIR;ZMIR;bob  
BBB;ANKR;RRRR;ABC   

for row == 2 and column == 2
perl -a -F\; -pe 's/$F[1]/***/ if $. == 2' your-file

123;IZMIR;ZMIR;123  
abc;***;aaa;999  
AAA;ZMIR;ZMIR;bob  
BBB;ANKR;RRRR;ABC    

---

Also without -a -F
perl -pe 's/123/***/ if $. == 1' your-file

output

***;IZMIR;ZMIR;123  
abc;ANKAR;aaa;999  
AAA;ZMIR;ZMIR;bob  
BBB;ANKR;RRRR;ABC   

---

If you want to edit you can add -i option that means Edit in-place And that's it, it simply find, replace and save in the same file
perl -i -a -F\; and so on

Answer 5

You need to include some absolute references in the line:

• ^ for beginning of the line
• unequivocal separation pattern
• ^.*ZMIR and [^;]*;ZMIR give different values where first take everything before ZMIR and sed take the longest possible

Specific

sed 's/^\([^;]*;[^;]*;\)ZMIR;/\1IZMIR;/' YourFile

generic where Old and New are batch variable (Remember, this is regex value so regex rules to apply like escaping some char)

#Old='ZMIR'
#New='IZMIR'

sed 's/^\(\([^;]*;\)\{2\}\)'${Old}';/\1'${New}';/' YourFile

In this simple case sed is an alternative, but awk is better for a complex or long line.