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command block {..}  [ganging a bunch of commands]
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Sometimes you want to simply gang up a bunch of commands. This is usually
motivated to avoid typing a new line.

e.g.

$ a=2
$ [[ a -eq 1 ]] && {echo hello; echo kitty}

This may look obvious but try the following to appreciate the value {}

$ [[ a -eq 1 ]] && echo hello; echo kitty

However, here is some Unix subtlety/arcana. Say, you want a shell
script which quits if a=1 but not otherwise.

Then 
$ cat tryit
#!/bin/bash
[[ a -eq 1 ]] && {echo "I quit because a=1"; exit -1}

$ export a=1
$ ./tryit    #will not compile

You MUST have "{ " and ";}\n" as in

$ cat tryit
#!/bin/bash
[[ a -eq 1 ]] && { echo "I quit because a=1"; exit -1;}