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# 1  
Old 06-13-2019
Use sed commands on multiple lines

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

need some help with this

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


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

Last edited by Scrutinizer; 06-14-2019 at 06:17 AM.. Reason: code tags correction
# 2  
Old 06-13-2019
You can add line number like this to run substitute only on first line
sed -i "1{s/{+//;s/+}//;}" error.txt

# 3  
Old 06-13-2019
Try also
sed '1bL; 10bL; b; :L; p; s/{+\|+}\|\[-.*-]//g;' file

EDIT: removed p; leftover from testing / debugging:

sed '1bL; 10bL; b; :L; s/{+\|+}\|\[-.*-]//g;' file

Last edited by RudiC; 06-14-2019 at 06:23 AM..
# 4  
Old 06-14-2019
cant i use a variable instead of that 1?
# 5  
Old 06-14-2019
Yes but use double quotes for variable substitution
sed "${var}..." file

# 6  
Old 06-14-2019
Originally Posted by utkarshkhanna44
cant i use a variable instead of that 1?
In principle you can, but sed uses a lot of characters with a special meaning to the shell. Therefore, to protect the shell from reading it, sed-commands are usually enclosed in single-quotes:

sed '<...sed-commands...> ' /some/file

This, in turn, has a side effect: the shell ignores anything inside single-quotes and hence variables are not expanded. If you write something like:

command $var

then prior to executing the line the shell replaces "$var" with the content of the variable. This is not the case inside single quotes. You can use double quotes instead ("), but this may have side effects too (i.e. "*" means something to the shell it might expand it), therefore you should use a mix of single- and double-quoting:

sed '<...sed-commands...> '"$var"'<...more sed-commands...>' /some/file

This looks cumbersome at first but offers the best protection and the most robustness. Notice that your variables can contain i.e. numbers and other simple things but under no circumstances you should put parts of regexps and special characters into your variables! Even if it works this is a great recipe for disaster.

I hope this helps.

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