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ortiga
Asked: 2020-01-31 12:56:51 +0800 CST 2020-01-31 12:56:51 +0800 CST

How do I join all the lines into one?

  • 772

I have the following code:

#!/bin/bash

FSTAB=` grep -v "^#" /etc/fstab | grep . | grep -v "swap" | grep -v "UUID"   | awk '{print $1,$2,$3}'`

for i in $FSTAB
do
    echo "$i"
done

this returns me:

/dev/mapper/centos-root
/
xfs
/dev/sdb2
/hdos
xfs

The problem is that later I want to compare it, so it is returning it to me with line breaks and I want it to return it to me in a single line without breaks, that is to say:

/dev/mapper/centos-root / xfs /dev/sdb2 /hdos xfs
bash

2 Answers

  1. If the result returned by a simple echo "$FSTAB"is

    /dev/mapper/centos-root
/
xfs
/dev/sdb2
/hdos
xfs

    So you can remove or replace the "\n" line breaks with tr.

    $ echo "$FSTAB" | tr '\n' ' '

    Or withsed

    $ echo "$FSTAB" | sed ':a;N;$!ba;s/\n/ /g'

    The explanation (which I don't know) can be found in another answer .

    In both cases, the loop foris unnecessary.

    And now we are all on the train awk, an option that I think is viable is:

    $ egrep -v "^#|(swap|UUID)" fstab | awk '{for (i=1; i<=3; i++){printf $i" "}}'
/dev/sda1 / ext4 /dev/sda3 /home ext4 LABEL=cloudimg-rootfs / ext3 /dev/mapper/centos-root / xfs

    From a file of the form.

    # <device>        <dir>        <type>        <options>        <dump> <fsck>
/dev/sda1         /            ext4          noatime          0      1
/dev/sda2         none         swap          defaults         0      0
/dev/sda3         /home        ext4          noatime          0      2
UUID=881350dc-1eef-47b4-bec4-199454179b4e / ext3 defaults 1 1
LABEL=cloudimg-rootfs / ext3 defaults 1 1
/dev/mapper/centos-root / xfs defaults 1 1

    Or traversing the array of fields.

    $ egrep -v "^#|(swap|UUID)" fstab | awk '{NF-=3; printf "%s " ,$0}'

    Or furthermore, following the advice of next.

    $ awk '/^#|(swap|UUID)/{ next; }{NF-=3; printf "%s " ,$0}' fstab

    Or better by negating the regex.

    $ awk '!/^#|(swap|UUID)/{NF-=3; printf "%s " ,$0}' fstab

    Which you can also solve with cutand xargs.

    $ egrep -v "^#|(swap|UUID)" fstab | tr -s " " | cut -d " " -f 1-3 | xargs
    • 2
  2. Best Answer

    Since you're using awk, you can let it do it itself, preventing it from adding a line break at the end of each one. change

    awk '{print $1,$2,$3}'

    by

    awk '{printf "%s %s %s",$1,$2,$3}'

    And, continuing with awk, you can simplify all those command interconnections:

    FSTAB=`awk '/^#/{next} /swap/{next } /UUID/{next} {printf "%s %s %s",$1,$2,$3}'`

    The syntax /EXPRESION-REGULAR/{ ... }executes the code only if the regular expression matches, while {next}discarding the current line to continue with the next.

    • 2