CODEWITHSUNDEEP
linuxunixsed
Micael Illos
Micael Illos

Reputation: 492

Swapping the first word with itself 3 times only if there are 4 words only using sed

Hi I'm trying to solve a problem only using sed commands and without using pipeline. But I am allowed to pass the result of a sed command to a file or te read from a file. EX:

sed s/dog/cat/ >| tmp 
or
sed s/dog/cat/ < tmp

Anyway lets say I had a file F1 and its contents was :

Hello hi 123
if a equals b
you
one abc two three four
dany uri four 123

The output should be:

if if if a equals b
dany dany dany uri four 123

Explanation: the program must only print lines that have exactly 4 words and when it prints them it must print the first word of the line 3 times.

I've tried doing commands like this: 

sed '/[^ ]*.[^ ]*.[^ ]*/s/[^ ]\+/& & &/' F1

or

sed 's/[^ ]\+/& & &/' F1

but I can't figure out how i can calculate with sed that there are only 4 words in a line. any help will be appreciated

Upvotes: 3

Views: 108

Answers (2)

ctac_
ctac_

Reputation: 2491

If the fields are tab separated

sed 'h;s/[^[:blank:]]//g;s/[[:blank:]]\{3\}//;/^$/!d;x;s/\([^[:blank:]]*[[:blank:]]\)/\1\1\1/' infile

Upvotes: 1

Ed Morton
Ed Morton

Reputation: 204035

$ sed -En 's/^([^[:space:]]+)([[:space:]]+[^[:space:]]+){3}$/\1 \1 &/p' file
if if if a equals b
dany dany dany uri four 123

The above uses a sed that supports EREs with a -E option, e.g. GNU and OSX seds).

Upvotes: 4

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