GREP to retrieve different lines

[knob]

Good evening, could I retrieve both lines at the same time using grep (in one cmd line) ?
In other words, the first line (no matter the content) and all lines with THISLINE word.

for example :
Header line blabla....
line blabla.... blabla....
line THISLINE.... blabla....
line blabla.... blabla....
line blabla.... blabla....

the result :
Header line blabla....
line THISLINE.... blabla....

[WharfRat]

You can use egrep 'Header|THISLINE' /file/to/search

[knob]

thanks... anyway, how to pickup the first line instead of the word header ?

[syg00]

The grep manpage has a good write-up of elementary regex.
Some-how missed your followup q. That gets more difficult - I might move over to sed.

[TI58C]

Hi knob,

For problems like your 2nd question, I use awk. Try
awk '{if (NR==1 || $0 ~/THISLINE/){print}}'

In awk, every line is a record. What this awk statements do is: IF first record(=first line) OR(||) line($0) conforms to pattern (/THISLINE/) THEN print the line.

Patterns are regular expressions. They are invaluable when using grep / sed / tr / awk etc..

If you often have such problems, awk is very useful. To me it is like having a "mini-C" in bash/terminal.
And, unlike complicated sed expressions, You can actually read/understand them.

This is a good start with awk:
http://www.grymoire.com/Unix/Awk.html

And this for regexes:
http://www.grymoire.com/Unix/Regular.html

Kind regards,

Robert

btw:
WharfRat,
Believe egrep is old syntax, grep -E new/preferred?