Use sed commands on multiple lines

UNIX for Beginners Q & A
1

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

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

2

You can add line number like this to run substitute only on first line

sed -i "1{s/{+//;s/+}//;}" error.txt
3

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
4

cant i use a variable instead of that 1?

5

Yes but use double quotes for variable substitution

var=1
sed "${var}..." file
6

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.

bakunin

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