Understanding Bash if statement that invokes a command

Question

Does anyone know what this is doing:

if ! /fgallery/fgallery -v -j3 /images /usr/share/nginx/html/ "${GALLERY_TITLE:-Gallery}"; then
  mkdir -p /usr/share/nginx/html

I understand the first part is saying if /fgallery/fgallery directory doesn't exist but after this it it not clear for me.

Answer 1

In Bash, we can build an if based on the exit status of a command this way:

if command; then
  echo "Command succeeded"
else
  echo "Command failed"
fi

then part is executed when the command exits with 0 and else part otherwise.

Your code is doing exactly that.

It can be rewritten as:

/fgallery/fgallery -v -j3 /images /usr/share/nginx/html/ "${GALLERY_TITLE:-Gallery}"; fgallery_status=$?
if [ "$fgallery_status" -ne 0 ]; then
  mkdir -p /usr/share/nginx/html
fi

But the former construct is more elegant and less error prone.

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See these posts:

• How to conditionally do something if a command succeeded or failed
• Why is testing "$?" to see if a command succeeded or not, an antipattern?