Want to have a script to process screen prints as grep.
I can run it like: cat file.txt | my_script
Tried below script, it didn't print out anything.
#!/bin/bash
line=$@
echo $line
2 Answers
Same idea as @glemco's answer but this version should be safe for special characters (excluding a NULL byte):
#!/bin/bash
while IFS= read -r line
do
printf '%s\n' "$line"
done
IFS=is to prevent trimming the leading and trailing whitespace-ris used to prevent backslash escapes to be processed- The quotes
"around"$line"are to prevent glob expansion, and to prevent replacing whitespace sequences with a single space
You are trying to read from command line arguments ($@) while you should be reading from stdin.
Basically the pipe attaches the first command's stdout to the second's stdin.
A simple way how to do what you wanted in bash would be to use the read built-in command, line by line as in the example.
#!/bin/bash
while read line
do
echo $line
done
Of course you can do whatever you want instead of echo.
-
4A single
catas the body of the script would be safer, if you just want to pass the output through. Your code would remove flanking whitespace, multiple whitespace characters between words, and it would potentially also expand filename globbing patterns if these were fed into the script. Additionally,echomay interpret certain escape sequences, like\tand\netc.– Kusalananda ♦Commented Jul 15, 2021 at 9:54
greppurely as a shell script? Your script, if you invoke it like you show, does output something: an empty line.readto read fromstdin. If you want to use the data in another command, which reads from stdin, you can simply call it.cat /dev/stdinorgrep -o '.' /dev/stdin. Do not forget to specify the path to the script:./my_script