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Toodarday
Asked: 2020-10-14 02:48:01 +0800 CST

Add text but first check if it's present already prevent duplication

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I have a script that runs to fix any network issues

echo '            routes:' >> /etc/netplan/50-cloud-init.yaml
echo '            - to: 51.89.XXX.XXX/32' >> /etc/netplan/50-cloud-init.yaml
echo '              via: 0.0.0.0' >> /etc/netplan/50-cloud-init.yaml
echo '              scope: link' >> /etc/netplan/50-cloud-init.yaml
echo '            - to: 2XXX:41d0:XX0:XXff:ff:ff:ff:ff' >> /etc/netplan/50-cloud-init.yaml
echo '              scope: link' >> /etc/netplan/50-cloud-init.yaml

However how am I able to prevent it from running twice if those values are already set? I would like to script to check first if each of the lines are present and if they are then it will not add them.

text-processing

1 Answers

  1. The simplest way that comes to mind is to first issue a grep call for the text to be added on the file itself and then use the || ( OR ) operator and after that issue the echo ' ' >> call like so:

    grep '            routes:' /etc/netplan/50-cloud-init.yaml || echo '            routes:' >> /etc/netplan/50-cloud-init.yaml

    The text will be added only if it is not already present in the file.

    The command after || will only be executed if the command before it fails.

    This means if

    grep '            routes:' /etc/netplan/50-cloud-init.yaml

    fails to return a result which means the text is not in the file,

    then

    echo '            routes:' >> /etc/netplan/50-cloud-init.yaml

    Will be executed and the text will be added.

    Otherwise if the text is already in the file nothing will be added to it.

    This has to be used for each line of text you wish to check for before adding it.

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