Useless cat. Consider 'cmd < file | ..' or 'cmd file | ..' instead. Open
if ! cat /etc/hosts | grep "bbs.service.cf.internal" > /dev/null; then- Read upRead up
- Exclude checks
Useless cat. Consider 'cmd < file | ..' or 'cmd file | ..' instead.
Problematic code:
cat file | tr ' ' _ | nl
cat file | while IFS= read -r i; do echo "${i%?}"; doneCorrect code:
< file tr ' ' _ | nl
while IFS= read -r i; do echo "${i%?}"; done < fileRationale:
cat is a tool for con"cat"enating files. Reading a single file as input to a program is considered a Useless Use Of Cat (UUOC).
It's more efficient and less roundabout to simply use redirection. This is especially true for programs that can benefit from seekable input, like tail or tar.
Many tools also accept optional filenames, e.g. grep -q foo file instead of cat file | grep -q foo.
Exceptions
Pointing out UUOC is a long standing shell programming tradition, and removing them from a short-lived pipeline in a loop can speed it up by 2x. However, it's not necessarily a good use of time in practice, and rarely affects correctness. [[Ignore]] as you see fit.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Useless cat. Consider 'cmd < file | ..' or 'cmd file | ..' instead. Open
if ! cat /etc/hosts | grep "blobstore.service.cf.internal" > /dev/null; then- Read upRead up
- Exclude checks
Useless cat. Consider 'cmd < file | ..' or 'cmd file | ..' instead.
Problematic code:
cat file | tr ' ' _ | nl
cat file | while IFS= read -r i; do echo "${i%?}"; doneCorrect code:
< file tr ' ' _ | nl
while IFS= read -r i; do echo "${i%?}"; done < fileRationale:
cat is a tool for con"cat"enating files. Reading a single file as input to a program is considered a Useless Use Of Cat (UUOC).
It's more efficient and less roundabout to simply use redirection. This is especially true for programs that can benefit from seekable input, like tail or tar.
Many tools also accept optional filenames, e.g. grep -q foo file instead of cat file | grep -q foo.
Exceptions
Pointing out UUOC is a long standing shell programming tradition, and removing them from a short-lived pipeline in a loop can speed it up by 2x. However, it's not necessarily a good use of time in practice, and rarely affects correctness. [[Ignore]] as you see fit.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Useless cat. Consider 'cmd < file | ..' or 'cmd file | ..' instead. Open
if ! cat /etc/hosts | grep "uaa.service.cf.internal" > /dev/null; then- Read upRead up
- Exclude checks
Useless cat. Consider 'cmd < file | ..' or 'cmd file | ..' instead.
Problematic code:
cat file | tr ' ' _ | nl
cat file | while IFS= read -r i; do echo "${i%?}"; doneCorrect code:
< file tr ' ' _ | nl
while IFS= read -r i; do echo "${i%?}"; done < fileRationale:
cat is a tool for con"cat"enating files. Reading a single file as input to a program is considered a Useless Use Of Cat (UUOC).
It's more efficient and less roundabout to simply use redirection. This is especially true for programs that can benefit from seekable input, like tail or tar.
Many tools also accept optional filenames, e.g. grep -q foo file instead of cat file | grep -q foo.
Exceptions
Pointing out UUOC is a long standing shell programming tradition, and removing them from a short-lived pipeline in a loop can speed it up by 2x. However, it's not necessarily a good use of time in practice, and rarely affects correctness. [[Ignore]] as you see fit.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.