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user294015
Asked: 2018-04-17 03:39:05 +0800 CST

IFS to read systeminfos

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I tried to read some system infos and put them into variables:

df -k | grep /dev/mmcblk0p1 | IFS=" " read -r device blocks used available use_percent mounted_on

It did not work, all variables are empty.

bash ifs

2 Answers

  1. The issue is not the IFS, it's because in bash (and certain other shells) the RHS of a pipeline is executed in a subshell.

    A simple alternative is to use process substitution to keep the read in the parent shell:

    read -r device blocks used available use_percent mounted_on < <(df -k | grep /dev/mmcblk0p1)

    See Bash: Variable assignment doesn't seem to 'stick'

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  2. If you assign variables using read, these must be part of the same block statement { ... }:

     df -k | grep /dev/mmcblk0p1 | { 
   read -r device blocks used available use_percent mounted_on
   printf "device=%s\nblocks=%s\nused=%s\navailable=%s\nuse_percent=%s\nmounted_on=%s\n" $device $blocks $used $available $use_percent $mounted_on
}
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