Tag Archives: Command line

Touching files in Windows

In Unix you have the touch command which you can use to update a files timestamp. No such thing in Windows. But instead, apparently, one can do this:

REM Updates the timestamp of the file
copy /b filename.ext +,,

REM Creates a new empty file
echo $null >> filename.ext

If you need it more than seldom there are also some more tricks in the StackOverflow sources below.

Sources:
Windows equivalent of the Linux command ‘touch’?
Equivalent of Linux `touch` to create an empty file with PowerShell?

Unix: Remove lines from a file based on regular expression

Just a note to self. Useful for trimming away useless information from a log file for example.

# Output result
$ sed "/pattern/d" file.log

# Overwrite file
$ sed "/pattern/d" file.log > file.log

# Inplace deletion (requires GNU sed)
$ sed -i "/pattern/d" file.log

In the pattern, things like capturing groups and alternations needs to be escaped with a slash, \. If you have RegexBuddy you can use the GNU BRE flavor to help you construct the pattern.

Source: StackOverflow

Unix: Command history search

In a Unix Bash shell we can scroll through previous commands by using the up and down arrow keys, but we can also search for previous commands. I keep forgetting how, so time to write it down 😛

Ctrl+r

Start a command search

Run the command directly
Ctrl+e or Ctrl+a

Exit search and jump to the end or beginning of command.
or

Exit search and move through command as usual
Ctrl+k

Remove everything after the current cursor position and to the end of the command

Bat: Some simple things to make batch scripts more helpful

Tried to make a helpful batch script for something at work and learned some new things I thought I’d write down here so I know where to find it later.

Turn off echoing

Should be known by everyone really, but in case you don’t. Prevents the commands in the batch script and the command prompt to show up while the script is running. Beginning a line with @ does this for a single command.

@echo off

Comments

REM Some comment
REM Will still appear as a command if you haven't disabled echoing

Labels and goto

Trivial, but I keep forgetting about this since I never use it in other programming.

goto end
REM Will be skipped
:end

Set title of command prompt

title MyScript: Doing x now

Check command line arguments

if "%~1"=="" (echo Usage: test.bat path && goto end)
if not exist %~1 (echo %~1 does not exist && goto end)

Simpe choices

choice /c ny /n /d y /t 10 /m "Do you really want to do this? [y=10s,n]
if ERRORLEVEL 2 (
    echo Ok, I'll do it
)

Run other batch scripts

If you don’t use the call command, the other script will actually take over and your script will end.

call other.bat arg1 arg2 ...

Do the same thing with various subjects

for %%x in (
    a
    b
    c
) do (
    echo %%x
)

Unix: Useful and pretty prompt

Some servers at work has varying degrees of useful prompts when I connect to them through SSH. Usually they are quite annoying and for example showing the shell type and version, which I frankly don’t care much about. Here’s how to make it show the current user, hostname and working directory. In addition the hostname is made more visible, which is a nice effect.

$ bold=$(tput bold)
$ reset=$(tput sgr0)
$ export PS1="\u@\[$bold\]\h\[$reset\]:\w\$ "

Stick it in your .profile, .bash_profile or whatever else you’ve got going on to make it more permanent.

Quick’ish way to swap between Java versions on Windows

Here’s a sort of quick way to swap between Java versions on Windows without having to change any environment variables and restarting your console window and such. The short version is to create symlinks to your java versions and then a single symlink called for example ‘active’ which points to the one you want. In your environment variables java_home and path you’d then point to this ‘active’ symlink instead of the actual installation. You can then fairly quickly swap out the target of the ‘active’ symlink and, tadaa’ish, you have a different version.

Setup

  1. Open up an elevated command prompt.
  2. Go/Make somewhere you want this.
    > c:
    > mkdir \dev\java
    > cd \dev\java
  3. Set up the symlinks
    > mklink /d 1.5 "c:\Program Files\Java\jdk1.5.0_22"
    > mklink /d 1.7 "c:\Program Files\Java\jdk1.7.0"
    > mklink /d 1.6 "c:\Program Files\Java\jdk1.6.0_27"
    > mklink /d active 1.7
  4. Set your JAVA_HOME and PATH environment variables. *
    setx JAVA_HOME "C:\dev\java\active" /m
    setx PATH "%JAVA_HOME%\bin;%PATH%" /m
* The second command assumes you don’t have Java in your PATH already. If you do, you should edit it the usual way instead. Also note that if JAVA_HOME is already set, it will be expanded in the second command.

Now open up a new regular command prompt and run the following.

> java -version
> mvn --version

Both (skip mvn if you don’t have maven installed) should report Java version 1.7.

Swapping

So, let’s say we want to change to java 1.5, we just need to run the following in an elevated command prompt.

> cd \dev\java
> rmdir active && mklink /d active 1.5

If you now repeat the version checks we did in our regular command prompt they should both report version 1.5 instead of 1.7. And we didn’t even have to restart the command prompt.

Shortcut

To prevent us from having to do this manually we could also create a simple bat file. I made one I called swap.bat which I put in the same directory as the symlinks with the following contents.

@echo off
cd \dev\java && rmdir active && mklink /d active %~1

You could then create a short cut to for example c:\dev\java\swap.bat 1.5, set it to run as administrator, and you’d have a two click solution to change the Java version to 1.5. I created one shortcut for each version.

If you have a better way, please leave a comment though. Always on the lookout for things and techniques that can make my developer life simpler 🙂

Pretty print XML on Unix command line

Needed to check some XML output from a CalDAV service so I used curl, which is nice and simple. Only problem was that all the XML came back on a single long unreadable line. Turned out it wasn’t too difficult to get it formatted:

$ curl --digest --user usr:pwd -X PROPFIND  | xmllint --format -

The key part here is of course the piping into xmllint. --format tells it to format the XML and the - tells it to read the XML from standard in. The dash can be swapped with the path to an XML file, if you need to format already downloaded XML.

$ xmllint --format file.xml

Simple pimple dimple 🙂