如何使用grep / awk / sed将字符添加到特定行

Question

I want to search a file and add \\1 to the end of every line that begins with @. One issue is grep doesn't like "\\1". This is a few lines of how the file looks:

@SRR1248080.1 1 length=90
TCTCACTGGCTGACTGAAGGCATGTCTAGTATTCAGAGTTTGCTACGATTTGGTACCGCTTTCGCAGCCC
GCACCGAAACAGTGCTTTACCCCTAGACAGCTCATAGTCAACCGCTGCGCCTCAACGCATTTCGGGGAGA
ACCAGCTAGCTCCGAGTTCGATTGGTATTTCACCCCTAACCACAGCTCATCCGCTGATTTTTCAACATCA
@SRR1249238.1 1 length=173
GCACCGAAACAGTGCTTTACCCCTAGACAGCTCATAGTCAACCGCTGCGCCTCAACGCATTTCGGGGAGA
ACCAGCTAGCTCCGAGTTCGATTGGTATTTCACCCCTAACCACAGCTCATCCGCTGATTTTTCAACATCA

I'd like it to read:

@SRR1248080.1 1 length=90\1
TCTCACTGGCTGACTGAAGGCATGTCTAGTATTCAGAGTTTGCTACGATTTGGTACCGCTTTCGCAGCCC
GCACCGAAACAGTGCTTTACCCCTAGACAGCTCATAGTCAACCGCTGCGCCTCAACGCATTTCGGGGAGA
ACCAGCTAGCTCCGAGTTCGATTGGTATTTCACCCCTAACCACAGCTCATCCGCTGATTTTTCAACATCA
@SRR1249238.1 1 length=173\1
GCACCGAAACAGTGCTTTACCCCTAGACAGCTCATAGTCAACCGCTGCGCCTCAACGCATTTCGGGGAGA
ACCAGCTAGCTCCGAGTTCGATTGGTATTTCACCCCTAACCACAGCTCATCCGCTGATTTTTCAACATCA

Answer 1

Adding \\1 to the end of every line that begins with a @ is bread & butter for sed . You simply specify a regular expression matching the lines to modify, and you can use an s command to sub in your tail for the zero-length end of line:

sed '/^@/ s/$/\\1/' input_file

Note the doubling of the backslash to suppress its special meaning to sed .

You might want to skip subbing lines that have already been subbed, perhaps by a previous run. That's not hard either: just match those lines and use an n command to output them without further processing:

sed '/\\1$/ n; /^@/ s/$/\\1/' input_file

Note that the sed script is enclosed in single quotes, not double quotes; it makes a difference (to the shell) here.

Answer 2

@aeli: Try(if you are interested in awk solution) too:

awk '/^@/{print $0"\\1";next} 1'  Input_file

It is simple, look for a line which is getting started from @ if yes then print complete line along with "\\1" and do next(means skip all other mentioned actions). Mentioning 1 means: in awk it works on condition then action method, so I am putting 1 here which is making condition TRUE here and mentioning no actin here so by default print of current line will happen.