在Linux上使用AWK写入文件

Question

I have a file that has several lines of which one line is

-xxxxxxxx()xxxxxxxx

I want to add the contents of this line to a new file

I did this :

awk ' /^-/ {system("echo" $0 ">" "newline.txt")} '

but this does not work , it returns an error that says :

Unnexpected token '(' 

I believe this is due to the () present in the line. How to overcome this issue?

Answer 1

You don't need the system , echo commands, simply:

awk '/^-/ {print $1}' file > newfile

This will capture lines starting with - and truncate the rest if there's a space.

awk '/^-/ {print $0}' file > newfile

Would capture the entire line including spaces.

You could use grep also:

grep -o '^-.*' file > newfile

Captures any lines starting with -

grep -o '^-.*().*' file > newfile

Would be more specific and capture lines starting with - also containing ()

Answer 2

First of all for simple extraction of patterns from file, you do not need to use awk it is an overkill, grep would be more than enough for the task:

INPUT:

$ more file
123
-xxxxxxxx()xxxxxxxx
abc
-xyxyxxux()xxuxxuxx
123
abc
123

command:

$ grep -oE '^-[^(]+\(\).*' file                                                                                                  
-xxxxxxxx()xxxxxxxx
-xyxyxxux()xxuxxuxx

explanations:

Option: -oE to define the output as the pattern and not the whole line (can be removed) Regex: ^-[^(]+\\(\\).* will select lines that starts with - and contains ()

You can redirect your output to a new_file by adding > new_file at the end of your command.

Answer 3

You need to add proper spaces!

With your erronous awk ' /^-/ {system("echo" $0 ">" "newline.txt")} ' , the shell command is essentially echo-xxxxxxxx()xxxxxxxx>newline.txt , which surely doesn't work. You need to construct a proper shell command inside the awk string, and obey awk s string concatenation rules, ie your intended script should look like this (which is still broken, because $0 is not properly quoted in the resulting shell command):

awk '/^-/ { system("echo " $0 " > newline.txt") }'

However, if you really just need to echo $0 into a file, you can simply do:

awk '/^-/ { print $0 > "newline.txt" }'

Or even more simply

awk '/^-/' > newline.txt

Which essentially applies the default operation to all records matching /^-/ , whereby the default operation is to print , which is short for neatly printing the current record, ie this script simply filters out the desired records. The > newline.txt redirection outside awk simply puts it into a file.