It's quite easy to capture the output of a command and assign it in a shell's variable:
day=$(date +%d)
month=$(date +%m)
But, what if we want to perform the same task with just one program invocation? Here comes the power of eval! date(1) outputs a string like "day=29; month=07; year=11" (notice the semicolons I added on purpose at date's custom output) which is a legal shell line. This like is then parsed and executed by the shell once again with the help of eval. Just setting 3 variables!
Inspired by LinuxJournal's column "Dave Taylor's Work the Shell".
Show Sample Output
In order to create, let's say, 10 directories with a single process we can use the command:
mkdir test{1,2,3,4,5,6,7,8,9,10}
something extremely boring to type! Why not use seq?
seq -s, 1 10
and use its output inside the curly braces?
The obvious solution
mkdir test{$(seq -s, 1 10)}
is, unfortunately, too naive and doesn't work. The answer is the order of the shell expansions (feature of Bourne Shell, actually), where brace expansion happens before command substitution (according to Bash's manual).
The solution is to put another level of substitution, using the powerful and mystic command eval.
I found the trick in a similar problem in the post at http://stackoverflow.com/questions/6549037/bash-brace-expansion-in-scripts-not-working-due-to-unwanted-escaping
Nothing special about hashing here, only the use of cut, I think, could result at fewer keystrokes. Show Sample Output
If the problem is an aliased synonym for a command, you can still execute the original command by pre-pending it with a reverse-slash '\'. This works at least in Bash, but I guess the aliasing system refers definitely to Bash (and not only).
Better tool for exporting git's repository is Git itself!
commandlinefu.com is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.
Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.
» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10
Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):
Subscribe to the feed for: