Selecting specific variable in log file

UNIX for Beginners Q & A
1

Hi there

I am trying to look for a specific word in the log file and I am aware this can be done by grep for example.

As there will be multiple entries for this I want to grep the last one to enter the log... how would I go about this - would I have to use tail?

Thanks in advance

Alex

2

Did you try:

grep pattern filename | tail -1
3

How about

tac file | grep -m1 pattern

? It will save reading / searching through the entire file, esp. interesting for large files.

4

tac does read the entire file.?
With sed

sed -n '/pattern/x;$x;$p' file
5

No, it doesn't. When grep stops reading the pipe because it found the pattern and exited, tac fills it until it's full and then is killed with SIGPIPE:

lseek(3, 311877632, SEEK_SET)           = 311877632
read(3, "rag\nTestbeitrag\nTestbeitrag\nTest"..., 8192) = 8192
write(1, "itrag\nTestbeitrag\nTestbeitrag\nTe"..., 4096) = -1 EPIPE (Broken pipe)
--- SIGPIPE {si_signo=SIGPIPE, si_code=SI_USER, si_pid=4061, si_uid=1000} ---
+++ killed by SIGPIPE +++

As you can see, 311869440 (311877632 - 8192) bytes from the file have NOT been read.

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