Bash Space-Separated (e.g., --option argument
)
cat >/tmp/demo-space-separated.sh <<'EOF'
#!/bin/bash
POSITIONAL=()
while [[ $# -gt 0 ]]; do
key="$1"
case $key in
-e|--extension)
EXTENSION="$2"
shift # past argument
shift # past value
;;
-s|--searchpath)
SEARCHPATH="$2"
shift # past argument
shift # past value
;;
-l|--lib)
LIBPATH="$2"
shift # past argument
shift # past value
;;
--default)
DEFAULT=YES
shift # past argument
;;
*) # unknown option
POSITIONAL+=("$1") # save it in an array for later
shift # past argument
;;
esac
done
set -- "${POSITIONAL[@]}" # restore positional parameters
echo "FILE EXTENSION = ${EXTENSION}"
echo "SEARCH PATH = ${SEARCHPATH}"
echo "LIBRARY PATH = ${LIBPATH}"
echo "DEFAULT = ${DEFAULT}"
echo "Number files in SEARCH PATH with EXTENSION:" $(ls -1 "${SEARCHPATH}"/*."${EXTENSION}" | wc -l)
if [[ -n $1 ]]; then
echo "Last line of file specified as non-opt/last argument:"
tail -1 "$1"
fi
EOF
chmod +x /tmp/demo-space-separated.sh
/tmp/demo-space-separated.sh -e conf -s /etc -l /usr/lib /etc/hosts
Output from copy-pasting the block above
FILE EXTENSION = conf
SEARCH PATH = /etc
LIBRARY PATH = /usr/lib
DEFAULT =
Number files in SEARCH PATH with EXTENSION: 14
Last line of file specified as non-opt/last argument:
#93.184.216.34 example.com
Usage
demo-space-separated.sh -e conf -s /etc -l /usr/lib /etc/hosts
Bash Equals-Separated (e.g., --option=argument
)
cat >/tmp/demo-equals-separated.sh <<'EOF'
#!/bin/bash
for i in "$@"; do
case $i in
-e=*|--extension=*)
EXTENSION="${i#*=}"
shift # past argument=value
;;
-s=*|--searchpath=*)
SEARCHPATH="${i#*=}"
shift # past argument=value
;;
-l=*|--lib=*)
LIBPATH="${i#*=}"
shift # past argument=value
;;
--default)
DEFAULT=YES
shift # past argument with no value
;;
*)
# unknown option
;;
esac
done
echo "FILE EXTENSION = ${EXTENSION}"
echo "SEARCH PATH = ${SEARCHPATH}"
echo "LIBRARY PATH = ${LIBPATH}"
echo "DEFAULT = ${DEFAULT}"
echo "Number files in SEARCH PATH with EXTENSION:" $(ls -1 "${SEARCHPATH}"/*."${EXTENSION}" | wc -l)
if [[ -n $1 ]]; then
echo "Last line of file specified as non-opt/last argument:"
tail -1 $1
fi
EOF
chmod +x /tmp/demo-equals-separated.sh
/tmp/demo-equals-separated.sh -e=conf -s=/etc -l=/usr/lib /etc/hosts
Output from copy-pasting the block above
FILE EXTENSION = conf
SEARCH PATH = /etc
LIBRARY PATH = /usr/lib
DEFAULT =
Number files in SEARCH PATH with EXTENSION: 14
Last line of file specified as non-opt/last argument:
#93.184.216.34 example.com
Usage
demo-equals-separated.sh -e=conf -s=/etc -l=/usr/lib /etc/hosts
To better understand ${i#*=}
search for "Substring Removal" in this guide. It is functionally equivalent to `sed 's/[^=]*=//' <<< "$i"`
which calls a needless subprocess or `echo "$i" | sed 's/[^=]*=//'`
which calls two needless subprocesses.
Using bash with getopt[s]
getopt(1) limitations (older, relatively-recent getopt
versions):
- can't handle arguments that are empty strings
- can't handle arguments with embedded whitespace
More recent getopt
versions don't have these limitations. For more information, see these docs.
POSIX getopts
Additionally, the POSIX shell and others offer getopts
which doen't have these limitations. I've included a simplistic getopts
example.
cat >/tmp/demo-getopts.sh <<'EOF'
#!/bin/sh
# A POSIX variable
OPTIND=1 # Reset in case getopts has been used previously in the shell.
# Initialize our own variables:
output_file=""
verbose=0
while getopts "h?vf:" opt; do
case "$opt" in
h|\?)
show_help
exit 0
;;
v) verbose=1
;;
f) output_file=$OPTARG
;;
esac
done
shift $((OPTIND-1))
[ "${1:-}" = "--" ] && shift
echo "verbose=$verbose, output_file='$output_file', Leftovers: $@"
EOF
chmod +x /tmp/demo-getopts.sh
/tmp/demo-getopts.sh -vf /etc/hosts foo bar
Output from copy-pasting the block above
verbose=1, output_file='/etc/hosts', Leftovers: foo bar
Usage
demo-getopts.sh -vf /etc/hosts foo bar
The advantages of getopts
are:
- It's more portable, and will work in other shells like
dash
.
- It can handle multiple single options like
-vf filename
in the typical Unix way, automatically.
The disadvantage of getopts
is that it can only handle short options (-h
, not --help
) without additional code.
There is a getopts tutorial which explains what all of the syntax and variables mean. In bash, there is also help getopts
, which might be informative.
Yes, it is possible:
public class Foo {
private int x;
public Foo() {
this(1);
}
public Foo(int x) {
this.x = x;
}
}
To chain to a particular superclass constructor instead of one in the same class, use super
instead of this
. Note that you can only chain to one constructor, and it has to be the first statement in your constructor body.
See also this related question, which is about C# but where the same principles apply.
Best Answer
You can build an eclipse project via a workspace from the command line:
It uses the
jdt apt
plugin to build your workspace automatically. This is also known as a 'Headless Build'. Damn hard to figure out. If you're not using a win32 exe, you can try this:Update
Several years ago eclipse replaced
startup.jar
with the "equinox launcher"https://wiki.eclipse.org/Equinox_Launcher
On Eclipse Mars (MacOX):
The
-data
parameter specifies the location of your workspace.The version number for the equinox launcher will depend on what version of eclipse you have.