SED (regular expression) problem ---

[bluesmodular]

Hello,

I would like to replace Line 187 of my file named run_example.

The original line is below, including the spaces:


celldm(1) = 6.00,
I want it to become something like


celldm(1) = 6.05,
or


celldm(1) = 6.10,
where the number is stored in a variable called $bulksize . This variable increments properly in my for loop.

I tried doing this:


cat run_example | sed -e "187 s_ [a-z]*(1) = _& $bulksize,_" > run_example


Didn't work...

Thank you for your help!

[iponeverything]

I can do a simple line replace with awk if it helps..


cat run_example|awk 'NR == 187 {print "celldm(1) = 6.05,"; next} {print $0}'>run_example.new

[amauk]

Use sed's in-place flag to edit a file


sed -i "s|\(celldm(1) *= *\)[0-9]\+\.[0-9]\+|\1${bulksize}|" run_example

[BoneKracker]

No need to call 'cat'
sed 's/red/blue/' oldfile >newfileor
sed 's/red/blue/' <oldfile >newfile

[DaithiF]

another solution:

sed "s/[0-9.]\+,$/$bulksize,/" run_example

[bluesmodular]

Thanks all! I found a solution with printf and ed



half=....
bulksize=....
for i in */run_example; do
printf '187s/= [^,]*/= %s/\nwq\n' "$bulksize" | ed -s "$i"
half=....
bulksize=....
done

[BoneKracker]

without looking at this in detail, I'll just mention that if you're already working in the shell, it's often worth first trying to apply BASH features such as parameter substitution before defaulting to calling external tools.

Although there are many cased where you need more power, using such features or the shell's built-ins is more efficient than calling externals.

For example, one form of parameter substitution:

${$string/$substring_match/$replacement_substring}

Such might not be applicable here, but it's a useful rule-of-thumb to try the built-in capabilities of whatever you've already got loaded into memory before resorting to external utilities, and also to use what's smaller in preference to what's bigger (e.g. parameter substitution in preference to sed in preference to awk in preference to perl).

[bluesmodular]

Thanks all !!

Using printf and ed, how would I replace a line that contains only a number, e.g. 6.00, with another number stored in variable $bulksize or $half ?

I guess I don't understand all the parts in this regular expressionhttp://images.intellitxt.com/ast/adTypes/2_bing.gif (http://www.unix.com/#)
'187s/= [^,]*/= %s/\nwq\n'

I know 187 is the line number, the s after that is substitution, and ^, matches a comma in the beginning? Or anything that's not a comma? Not sure what the rest of it means... where can I find a good reference for this?

[sedawk]

Normally ^ is beginning of the line and $ is the end of a line.

But if the first character in []-brackets is a ^ it means
"not".