Nested loop for reading two files with bash [duplicate]

Question

I'm currently trying to use the following code to merge two input files:

for i in `cat $file1`; do
    for j in `cat $file2`; do
        printf "%s %s\n" "$i" "$j"
    done
done

Given files created as follows:

printf '%s\n' A B C >file1
printf '%s\n' 1 2 3 >file2

...my expected/desired output is:

A 1
B 2
C 3

But instead, the output I'm getting is:

A 1
A 2
A 3
B 1
B 2
B 3
C 1
C 2
C 3

How can this be fixed?

And btw: grab good reads: Why you don't read lines with "for" and How can I read a file (data stream, variable) line-by-line (and/or field-by-field)? — KamilCuk
– KamilCuk, Commented Jun 11, 2019 at 13:18

ennox · Accepted Answer · 2019-06-11 13:25:58Z

2

Possible by using the pr command from coreutils, also possible with other commands/tools like paste and also by Shell and AWK scripts. Least effort by using the commands from coreutils as only a few parameters are required on the commandline, like in this example:

pr -TmJS" " file1 file2

where:

-T turns off pagination
-mJ merge files, Joining full lines
-S" " separate the columns with a blank

edited Jun 11, 2019 at 13:25

answered Jun 11, 2019 at 13:18

ennox

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1 Comment

Charles Duffy Over a year ago

In How to Answer, note the section "Answer Well-Asked Questions", and the bullet point therein regarding questions which "have been asked and answered many times before".

KamilCuk · Accepted Answer · 2019-06-11 13:20:29Z

1

The following command will work:

paste -d' ' file1 file2

The paste coreutils utility merges files line by line. The -d options is used to specify the delimeter, ie. space here.

answered Jun 11, 2019 at 13:20

KamilCuk

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3 Comments

elias Over a year ago

Thank you so much !!!! It works . Do you know if there is any alternative way to get the same result with a loop ?

Charles Duffy Over a year ago

@KamilCuk, ...consider the usual chiding about answering an obvious duplicate to have taken place.

Charles Duffy Over a year ago

@elias, follow the "already has an answer here" links at the top of the question; you'll see many of the existing instances of this question have something like

while IFS= read -r line1 <&3 && IFS= read -r line2 <&4; do echo "Read $line1 from file-1 and $line2 from file-2"; done 3<file1 4<file2

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