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An amazing grep trick that I use all the time: The -e flag can be used to search for multiple terms. A blank -e will search for null. Thus: Lets assume we have

An amazing grep trick that I use all the time: The -e flag can be used to search for multiple terms. A blank -e will search for null. Thus: Lets assume we have a log file with a bunch of relevant stuff, I want to highlight my search term, BUT I also want to keep all the other lines around for context: $ dmesg ...SNIP... [2334597.539661] sd 1:0:0:0: [sdb] Attached SCSI removable disk [2334597.548919] sd 1:0:0:0: [sdb] 57280429 512-byte logical blocks: (29.3 GB/27.3 GiB) [2334597.761895] sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA [2334597.761900] sdb: detected capacity change from 0 to 57280429 [2334597.772736] sdb: [2334631.115664] sdb: detected capacity change from 57280429 to 0 ...SNIP... A simple grep, will only return the selected lines: $ dmesg | grep capacity [2334597.761900] sdb: detected capacity change from 0 to 57280429 [2334631.115664] sdb: detected capacity change from 57280429 to 0 But I want all lines: $ dmesg | grep --color -e capacity -e '' ...SNIP... [2334597.539661] sd 1:0:0:0: [sdb] Attached SCSI removable disk [2334597.548919] sd 1:0:0:0: [sdb] 57280429 512-byte logical blocks: (29.3 GB/27.3 GiB) [2334597.761895] sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA *[2334597.761900] sdb: detected capacity change from 0 to 57280429* [2334597.772736] sdb: *[2334631.115664] sdb: detected capacity change from 57280429 to 0* ...SNIP... The null trick also works well on directories with many small files, like /proc/ or /sys/. Say, for example, you wanted to get the filename and value of each file: $ grep -R '' /sys/module/iwlwifi/parameters/ /sys/module/iwlwifi/parameters/nvm_file:(null) /sys/module/iwlwifi/parameters/debug:0 /sys/module/iwlwifi/parameters/swcrypto:0 /sys/module/iwlwifi/parameters/power_save:N /sys/module/iwlwifi/parameters/lar_disable:N ...SNIP...

addingnumbers 5y ago
I always used "-e ^" the same way you're using a null string, to show all lines of the files, each prefixed with the path and filename. Are they equivalent or is there a caveat I should watch out for?
- likpok 5y ago
  Zsh (and possibly other shells?) will expand a raw ^ into filenames. '' is a little shorter than '^' if you have to quote it.
  - jolmg 5y ago
    > and possibly other shells? Years ago--I don't if it's still the case--but the fish shell used ^ to redirect stderr. EDIT: I remembered right: https://web.archive.org/web/20111111003423/http://fishshell.com/user_doc/index.html#syntax https://web.archive.org/web/20111111003423/http://fishshell.... but it seems it's no longer the case: fish> echo foo ^ bar foo ^ bar https://fishshell.com/docs/current/tutorial.html#pipes-and-redirections https://fishshell.com/docs/current/tutorial.html#pipes-and-r...
pjungwir 5y ago
I have this in my ~/bin, but I like your version even better!: grep --color "$1"'\|$'
throwawayboise 5y ago
Since you're probably (or at least often) pipelining this into "less" assuming there is more than one screenful of lines, why not just use the regexp searching/highlighting built into less?

addingnumbers 5y ago

I always used "-e ^" the same way you're using a null string, to show all lines of the files, each prefixed with the path and filename. Are they equivalent or is there a caveat I should watch out for?

likpok 5y ago
Zsh (and possibly other shells?) will expand a raw ^ into filenames. '' is a little shorter than '^' if you have to quote it.
- jolmg 5y ago
  > and possibly other shells? Years ago--I don't if it's still the case--but the fish shell used ^ to redirect stderr. EDIT: I remembered right: https://web.archive.org/web/20111111003423/http://fishshell.com/user_doc/index.html#syntax https://web.archive.org/web/20111111003423/http://fishshell.... but it seems it's no longer the case: fish> echo foo ^ bar foo ^ bar https://fishshell.com/docs/current/tutorial.html#pipes-and-redirections https://fishshell.com/docs/current/tutorial.html#pipes-and-r...

pjungwir 5y ago

I have this in my ~/bin, but I like your version even better!: grep --color "$1"'\|$'

throwawayboise 5y ago

Since you're probably (or at least often) pipelining this into "less" assuming there is more than one screenful of lines, why not just use the regexp searching/highlighting built into less?