Use sed command for particular lines

Question

I have a text file on a Linux machine and I want to run 3 sed commands for the lines entered by the user using a perl script. I am doing this manually till now.

The sed commands I have to use are :

sed -i "s/{+//" error.txt sed -i "s/+}//" error.txt sed -i "s/\[-.*-]//g" error.txt

error.txt is the file where I want to run these commands, but I want them to run on a particular line which I will enter.

Error.txt:

1:module counter ( clk, reset, enable, {+dat_out+} ); 4: input clk, [-reset ;-] {+reset, enable;+} 5: wire {+N69, N70, N71,+} N72, N73, N74, N75, N76, N77, N78, N79, N80, 10: EDFFX2AD \dat_out_sig_reg[0] ( [-.D(synopsis_unconnected),-] {+.D(N69),+} .E(N96), .CK(clk), .Q(dat_out[0]) 12: EDFFX2AD \dat_out_sig_reg[1] ( {+.D(N70),+} .E(N94), .CK(clk), .Q(dat_out[1]) 14: EDFFX2AD \dat_out_sig_reg[2] ( .D(N71), [-.E(synopsis_unconnected),-] {+.E(N92),+} .CK(clk), .Q(dat_out[2])

expected output:

1:module counter ( clk, reset, enable, dat_out ); 4: input clk, [-reset ;-] {+reset, enable;+} 5: wire {+N69, N70, N71,+} N72, N73, N74, N75, N76, N77, N78, N79, N80, 10: EDFFX2AD \dat_out_sig_reg[0] ( .D(N69), .E(N96), .CK(clk), .Q(dat_out[0]) 12: EDFFX2AD \dat_out_sig_reg[1] ( {+.D(N70),+} .E(N94), .CK(clk), .Q(dat_out[1]) 14: EDFFX2AD \dat_out_sig_reg[2] ( .D(N71), [-.E(synopsis_unconnected),-] {+.E(N92),+} .CK(clk), .Q(dat_out[2])

The codes are applied on Line 1 and Line 10. Please suggest something

Add some sample text from the file including the line(s) that you want to edit and the expected output. — Nasir Riley
– Nasir Riley, Commented Jun 13, 2019 at 11:33
If you're using a perl script to obtain user input, it's hard to see a good reason to shell out to sed for the substitutions — steeldriver
– steeldriver, Commented Jun 13, 2019 at 11:39
I will take the input that on which line number does the user want to use the sed command. — Coolstrike
– Coolstrike, Commented Jun 13, 2019 at 11:40
This looks like wdiff output. What is the overall issue you are solving? — Kusalananda
– Kusalananda ♦, Commented Jun 13, 2019 at 12:13

simlev · Accepted Answer · 2019-06-13 13:36:39Z

You can specify a condition in the form of e.g a search pattern:

sed -i -r '/^10?:/ {s/\{\+//; s/\+}//; s/\[-.*-]//g}' error.txt

The substitutions are performed only if the line starts with 1: or 10:. This is the output:

1:module counter ( clk, reset, enable, dat_out ); 4: input clk, [-reset ;-] {+reset, enable;+} 5: wire {+N69, N70, N71,+} N72, N73, N74, N75, N76, N77, N78, N79, N80, 10: EDFFX2AD \dat_out_sig_reg[0] ( .D(N69), .E(N96), .CK(clk), .Q(dat_out[0]) 12: EDFFX2AD \dat_out_sig_reg[1] ( {+.D(N70),+} .E(N94), .CK(clk), .Q(dat_out[1]) 14: EDFFX2AD \dat_out_sig_reg[2] ( .D(N71), [-.E(synopsis_unconnected),-] {+.E(N92),+} .CK(clk), .Q(dat_out[2])

The condition can be on line numbers: this will only process the first line:

sed -i -r '1 {s/\{\+//; s/\+}//; s/\[-.*-]//g}' error.txt

Since you mention Perl, you might prefer to use the following:

perl -i -pe 'if (/^10?:/) {s/\{\+//; s/\+}//; s/\[-.*-]//g}' error.txt

or:

perl -i -pe 'if ($.==1 or $.==10) {s/\{\+//; s/\+}//; s/\[-.*-]//g}' error.txt

For this code sed -i -r '1 {s/\{\+//; s/\+}//; s/[-.*-]//g}' error.txt ; Cant I use variable instead of 1? like $var=1 sed -i -r '$var {s/\{\+//; s/\+}//; s/[-.*-]//g}' error.txt — Coolstrike
– Coolstrike, Commented Jun 14, 2019 at 6:14
@Coolstrike Yes, you can use a variable, but you should edit your post with the exact question and requirements. It seems that you are exposing only a part of a bigger problem: if you want better answers you should give a more comprehensive picture (as was suggested in the comments). — simlev
– simlev, Commented Jun 14, 2019 at 7:22

John Goofy · Accepted Answer · 2019-06-14 15:13:01Z

You can add a line or an range befor your sed command.

For your first example you can try for the 3rd line wich is numbered as #4:

sed "3 s/{+//" error.txt

Or if you need a script, you could work on this snippet:

#!/bin/bash echo -e "Usage:\t ./my_sed.sh linenumber file\n" sed "$1 s/{+//" $2

Can't I use a user input say a variable and then apply on the varaible value — Coolstrike
– Coolstrike, Commented Jun 14, 2019 at 4:51
Of course! You need to write a script to achive this. Review my edit, I give you a hint. — John Goofy
– John Goofy, Commented Jun 14, 2019 at 15:09

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