Is it possible to read a variable from a file and use in a Sh script

You could use below command sequence:

HWADDR=$( . /etc/sysconfig/network-scripts/ifcfg-eth0 ; echo $HWADDR)

Hi PJ,

I think noci's quite elegant solution will work if ifcfg-eth0 contains nothing which causes ifcfg-eth0 not to execute as a script (since he runs it as one).  His solution will also set any other environment variables assigned in the ifcfg-eth0 file.  If that's not good for you, here's an alternative way to do it:

==> ifcfg-eth0 <==
HWADDR=01:23:45:67:89
anything else

==> gatherdata <==
#!/bin/bash
HWADDR=$(perl -ne 'print $1 if /^HWADDR=(..:..:..:..:..)$/' ifcfg-eth0)
echo "HWADDR = '$HWADDR'"

Here's how it runs:
$ ./gatherdata
HWADDR = '01:23:45:67:89'

Thanks noci,
I guess that will be fine then, and I think I was mistaken where I said your "solution will also set any other environment variables assigned in the ifcfg-eth0 file", because the assignments will be done in a $(sub-shell), so will be forgotten immediately.
Nice work!

Question for noci: Is it possible for there to be any spaces (or other strange characters) in the assignments in the ifcfg-eth0 file, which might make it crash?  For example, this would fail:
VARIABLE=123 456

There might be spaces  before variable names, or after the value, as these files are mostly genereated during system setup there mostly are no spaces...
Here is an example:

DEVICE=eth0
TYPE="Ethernet"
ONBOOT="yes"
USERCTL="no"
BOOTPROTO="static"
IPADDR="192.168.1.235"
NETMASK="255.255.255.0"
HWADDR="00:15:5d:01:16:35"

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In this one no trailing spaces, usage in ifup:
ifup call ifup-eth which does:

....
CONFIG=${1}

need_config "${CONFIG}"

source_config
....

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Source config is somewhat more complex:

source_config ()
{
    CONFIG=${CONFIG##*/}
    DEVNAME=${CONFIG##ifcfg-}
    . /etc/sysconfig/network-scripts/$CONFIG
    [ -r "keys-$DEVNAME" ] && . /etc/sysconfig/network-scripts/keys-$DEVNAME
    case "$TYPE" in
    Ethernet)
        DEVICETYPE="eth"
        ;;
    CIPE)
        DEVICETYPE="cipcb"
        ;;
    IPSEC)
        DEVICETYPE="ipsec"
        ;;
    Modem)
        DEVICETYPE="ppp"
        ;;
    xDSL)
        DEVICETYPE="ppp"
        ;;
    ISDN)
        DEVICETYPE="ippp"
        ;;
    Wireless)
        DEVICETYPE="eth"
        ;;
    "Token Ring")
        DEVICETYPE="eth"
        ;;
    CTC)
        DEVICETYPE="ctc"
        ;;
    GRE | IPIP | IPIP6)
        DEVICETYPE="tunnel"
        ;;
    SIT | sit)
        DEVICETYPE="sit"
        ;;
    InfiniBand | infiniband)
        DEVICETYPE="ib"
        ;;
    OVS*)
        DEVICETYPE="ovs"
        ;;
    esac
    if [ -n "$HWADDR" ]; then
        HWADDR=$(echo $HWADDR | awk '{ print toupper($0) }')
    fi
    if [ -n "$MACADDR" ]; then
        MACADDR=$(echo $MACADDR | awk '{ print toupper($0) }')
    fi
    [ -z "$DEVICE" -a -n "$HWADDR" ] && DEVICE=$(get_device_by_hwaddr $HWADDR)
    [ -z "$DEVICETYPE" ] && DEVICETYPE=$(echo ${DEVICE} | sed "s/[0-9]*$//")
    [ -z "$REALDEVICE" -a -n "$PARENTDEVICE" ] && REALDEVICE=$PARENTDEVICE
    [ -z "$REALDEVICE" ] && REALDEVICE=${DEVICE%%:*}
    [ -z "$SYSCTLDEVICE" ] && SYSCTLDEVICE=${REALDEVICE/.//}
    if [ "${DEVICE}" != "${REALDEVICE}" ]; then
        ISALIAS=yes
    else
        ISALIAS=no
    fi
    if is_nm_running && [ "$REALDEVICE" != "lo" ] ; then
        nm_con_load "$CONFIG"
        if ! is_false $NM_CONTROLLED; then
            UUID=$(get_uuid_by_config $CONFIG)
            [ -n "$UUID" ] && _use_nm=true
        fi
    fi
}

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Hi noci & tel2

Thank you for taking the time to help, really appreciate it

@noci, I've just tried your suggestion. First I had to make ifcfg-eth0 executable.
Then I tried the following

HWADDR=""
HWADDR=$(  /etc/sysconfig/network-scripts/ifcfg-eth0 ; echo $HWADDR)
echo "$HWADDR"

I had to remove the dot in-front of the path name to find the file
I seem to be getting an empty variable as I'm seeing a blank line when I echo "$HWADDR"

Any ideas?

@ noci

just tried HWADDR=$(  grep HWADDR=  /etc/sysconfig/network-scripts/ifcfg-eth0 |  sed 's/^HWADDR=//' )

and that worked a treat, thank you very much

Eh. you DONT need to set the script executable. is it SHOULD not be executed but read.


you missed the '.'  space   isn't './etc...' but '.' SPACE '/etc/....'
before the script name wich means 'source' .
 (read the file, not execute the file). The FIRST DOES work is might be slightly more effective.

It could be rewritten as:

HWADDR=$( source /etc/sysconfig/network-scripts/ifcfg-eth0 ; echo $HWADDR)