Re: Post-grep-like operations

On 10 Dec 2005 at 16:31, Rob Simpson wrote:

> I am wanting to select lines containing 'fruit' or 'veg',

   This will select those lines. The \| represents OR:
   /fruit\|veg/

   This will select all the lines that do NOT contain those terms:
   /fruit\|veg/!

> and then
> carry out some operation on them, say substitution X for a.
[ ...]

> I am trying to do this in a sed file:
> 
> /fruit/b
> /veg/b
> d
> s/a/X/g
> 
> using the grep like command in the one-liners document.

   Well, you've come to the right group! (smile)

> The last expression doesn't get carried out.

   because the b command branches to the END of the script, not to 
the last line of the script.

> I can't find '/b' in the documentation.

   That's because /b isn't a switch, it's a command. In a structure 
like this:

    /abc/d

the 'd' is a command that operates on the pattern /abc/. In this 
case, 'd' is a real command (delete). But in a script like this:

    s/ab/c/d

the 'd' is a switch that modifies the s/// command. And I should add 
that there is no 'd' switch to the s/// command. Sed operates a 
little like awk in that it follows a

    /pattern/ command

syntax, except that sed doesn't require curly braces for every single 
one-line command, like awk does.

> Any help much appreciated,

    Try this:

    sed '/fruit\|veg/!d; s/a/X/g' file

In detail,

   /fruit\|veg/!d;  # If term is not found, delete the line
   s/a/X/g;         # On remaining lines, do the substitution


Hope this helps.

-- 
Eric Pement - pemente@xxxxxxxxxxxxx



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