I want to only do some code if $# equals 1 and $1 is a readable existing file.
I have following code:
if [[ $# -eq 1 ] -a [ test -r $1 ]]
I have tried many different solutions for an and statement.
Like
[ $# -eq 1 ] $$ [ test -r $1 ]
[ $# -eq 1 -a test -r $1 ]
and many more...
Nothing seems to work. I think its because of the test command.
Sometimes I get an error like test not found or too many arguments or smth else
My whole code:
#!/bin/bash
if [[ $# -eq 1 ] -a [ test -r $1 ]]
then
groupadd -f "TAI12A"
IFS=:
while read nachname vorname klasse
do
nutzername=$nachname$vorname
groupadd -f $klasse
useradd -g "TAI12A" -G $klasse -s /bin/bash -m -p "taipasswd $nutzername
done < $1
else
echo "Uebergabewerte fehlerhaft"
fi
if you want to use test, then no brackets:
if [ $# -eq 1 ] && test -r "$1" ; then
do this ...
fi
Note: [ is a command, it's an alias for test with one exception: when using [ instead of test, ] must be the last argument.
To illustrate this: even if bash nowadays includes [ as a builtin command, the command /usr/bin/[ should still exist on your server.
PS: I would just use:
if [ $# -eq 1 ] && [ -r "$1" ] ; then
do this ...
fi
which is the same as
if test $# -eq 1 && test -r "${1}" ; then
do this ...
fi
Further confusion might be added by the fact that bash also has an extended conditional expressions in the form [[ ... ]]. I recommend to read https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html#Bash-Conditional-Expressions
Related
I have a bash script and I want to check with an (el) if statement if a string is not in a file and then run an action
This is the part of the script:
elif [ "$(cat balance.txt)" -eq 250000000 ] && [ "$(find files/ -type f | wc -l)" -ge 5 ] && [ "$(grep -c "$(cat string.txt)" whitelist.txt)" -ge 1 ] && [ "$(grep -c "$(cat string.txt)" whitelist2.txt) " -eq 0 ] ;
then
sh result.sh
The first 2 parts of the elif statements are working but only the third part gives me problems:
[ "$(grep -c "$(cat string.txt)" whitelist2.txt) " -eq 0 ]
It skips this part and goes straight to the else part of the script which runs fine.
Does anybody maybe knows what I am doing wrong? Or what is should change?
I'm creating a bash script and somewhere inside I have this code:
if [ $# -eq 2 -a (! -r "$2" -o ! -f "$2") ]; then
echo "rvf: bestand \""$2"\" bestaat niet of is onleesbaar" 1>&2
exit 2
fi
When i try to run this inside the script I get this error:
Syntax Error (bash -n):
rvf: line 14: syntax error in conditional expression
rvf: line 14: syntax error near `-a'
rvf: line 14: `if [[ $# -eq 2 -a (! -r "$2" -o ! -f "$2") ]]; then'
How does '()' work inside Bash scripts?
[[ doens't support -a, and it is considered obsolete and non portable for [. The correct solution using [ would be
if [ "$#" -eq 2 ] && { [ ! -r "$2" ] || [ ! -f "$2" ]; }; then
Grouping is done with { ... } rather than ( ... ) to avoid creating an unnecessary subshell.
Using [[ is simplifies to
if [[ "$#" -eq 2 && ( ! -r "$2" || ! -f "$2" ) ]]; then
Parentheses can be used for grouping inside [[; as a compound command, it uses separate parsing and evaluation rules, compared to an ordinary command like [ (which is just an alias for test, not syntax of any kind).
In either case, De Morgan's laws lets you refactor this to something a little simpler:
if [ "$#" -eq 2 ] && ! { [ -r "$2" ] && [ -f "$2" ] }; then
if [[ "$#" -eq 2 && ! ( -r "$2" && -f "$2" ) ]]; then
There are multiple points of confusion here.
[ can (as an optional XSI extension to the standard) support ( as a separate word (meaning there needs to be spaces around it), but the POSIX sh specification marks it (like -a and -o) as "obsolescent" and advises against its use.
[[ does support (, but again, it needs to always be a separate word.
Don't do that at all, though. You're using only well-supported and portable functionality if you keep each test its own simple command and combine them only with the shell's boolean logic support.
That is:
if [ "$#" -eq 2 ] && { [ ! -r "$2" ] || [ ! -f "$2" ]; }; then
echo "rvf: bestand \"$2\" bestaat niet of is onleesbaar" >&2
exit 2
fi
Restructure your logic.
"Not A or Not B" is just a more complicated way to say "not (A and B)".
In bash, try
if [[ "$#" == 2 ]] && ! [[ -r "$2" && -f "$2" ]]; then
Better,
if [[ "$#" == 2 && -r "$2" && -f "$2" ]]
then : all good code
else : nope code
fi
Even better,
if [[ "$#" == 2 ]] # correct args
then if [[ -r "$2" ]] # is readable
then if [[ if -f "$2" ]] # is a file
then echo "all good"
: do all good stuff
else echo "'$2' not a file"
: do not a file stuff
fi
else echo "'$2' not readable"
: do not readable stuff
fi
else echo "Invalid number of args"
: do wrong args stuff
fi
Clear error logging is worth breaking the pieces out.
Even better, imho -
if [[ "$#" != 2 ]]
then : wrong args stuff
fi
if [[ ! -r "$2" ]]
then : unreadable stuff
fi
if [[ ! -f "$2" ]]
then : do not a file stuff
fi
: do all good stuff
I have to find a way to have my script read from one of these three options:
a file argument
standard input
a previously established environment variable
Here's what I currently have:
#!/bin/bash
key=$1
[ $# -ge 1 -a -f "$2" ] && input="$2" || [ -f "$INPUT" ] && input="$INPUT" || input="-"
echo $input
Only the environment variable refuses to work, the rest works fine.
I've tried using the export INPUT="pathnametofile" before but it doesn't make any difference, I end up with the shell asking me to enter info as if I called on cat.
The problem in your script
Your attemp is not working due to the way the shell processes a Lists of Commands:
‘&&’ and ‘||’ have equal precedence.
AND and OR lists are executed with left associativity.
Your sentence:
[ $# -ge 1 -a -f "$2" ] && input="$2" || [ -f "$INPUT" ] && input="$INPUT" || input="-"
does the same as follows:
[ $# -ge 1 -a -f "$2" ] && input="$2"
[ $? -eq 0 ] || [ -f "$INPUT" ]
[ $? -eq 0 ] && input="$INPUT"
[ $? -eq 0 ] || input="-"
Now yo may see why your unexpected behaviour.
A better attempt grouping commands
{ [ $# -ge 1 -a -f "$2" ] && input="$2"; } || { [ -f "$INPUT" ] && input="$INPUT"; } || input="-"
Now, due to precedence, the first group is not needed at all:
[ $# -ge 1 -a -f "$2" ] && input="$2" || { [ -f "$INPUT" ] && input="$INPUT"; } || input="-"
Furthermore, unless you have set the positional parameters by hand, you can remove the first check (after all, if $2 is emtpy, -f "" fails the same).
[ -f "$2" ] && input="$2" || { [ -f "$INPUT" ] && input="$INPUT"; } || input="-"
An alternative with the if conditional construct
if [ -f "$2" ]; then
input=$2
elif [ -f "$INPUT" ]; then
input=$INPUT
fi
echo "${input:=-}"
untested, but you'll probably have better luck with if commands, and test that the variable is not empty:
if [ $# -ge 1 -a -f "$2" ]; then
input="$2"
elif [ -n "$INPUT" -a -f "$INPUT" ]; then
input="$INPUT"
else
input="-"
fi
Often when writing for the bash shell, one needs to test if a file (or Directory) exists (or doesn't exist) and take appropriate action. Most common amongst these test are...
-e - file exists, -f - file is a regular file (not a directory or device file), -s - file is not zero size, -d - file is a directory, -r - file has read permission, -w - file has write, or -x execute permission (for the user running the test)
This is easily confirmed as demonstrated on this user-writable directory....
#/bin/bash
if [ -f "/Library/Application Support" ]; then
echo 'YES SIR -f is fine'
else echo 'no -f for you'
fi
if [ -w "/Library/Application Support" ]; then
echo 'YES SIR -w is fine'
else echo 'no -w for you'
fi
if [ -d "/Library/Application Support" ]; then
echo 'YES SIR -d is fine'
else echo 'no -d for you'
fi
➝ no -f for you ✓
➝ YES SIR -w is fine ✓
➝ YES SIR -d is fine ✓
My question, although seemingly obvious, and unlikely to be impossible - is how to simply combine these tests, without having to perform them separately for each condition... Unfortunately...
if [ -wd "/Library/Application Support" ]
▶ -wd: unary operator expected
if [ -w | -d "/Library/Application Support" ]
▶ [: missing `]'
▶ -d: command not found
if [ -w [ -d "/Library.... ]] & if [ -w && -d "/Library.... ]
▶ [: missing `]'
➝ no -wd for you ✖
➝ no -w | -d for you ✖
➝ no [ -w [ -d .. ]] for you ✖
➝ no -w && -d for you ✖
What am I missing here?
You can use logical operators to multiple conditions, e.g. -a for AND:
MYFILE=/tmp/data.bin
if [ -f "$MYFILE" -a -r "$MYFILE" -a -w "$MYFILE" ]; then
#do stuff
fi
unset MYFILE
Of course, you need to use AND somehow as Kerrek(+1) and Ben(+1) pointed it out. You can do in in few different ways. Here is an ala-microbenchmark results for few methods:
Most portable and readable way:
$ time for i in $(seq 100000); do [ 1 = 1 ] && [ 2 = 2 ] && [ 3 = 3 ]; done
real 0m2.583s
still portable, less readable, faster:
$ time for i in $(seq 100000); do [ 1 = 1 -a 2 = 2 -a 3 = 3 ]; done
real 0m1.681s
bashism, but readable and faster
$ time for i in $(seq 100000); do [[ 1 = 1 ]] && [[ 2 = 2 ]] && [[ 3 = 3 ]]; done
real 0m1.285s
bashism, but quite readable, and fastest.
$ time for i in $(seq 100000); do [[ 1 = 1 && 2 = 2 && 3 = 3 ]]; done
real 0m0.934s
Note, that in bash, "[" is a builtin, so bash is using internal command not a symlink to /usr/bin/test exacutable. The "[[" is a bash keyword. So the slowest possible way will be:
time for i in $(seq 100000); do /usr/bin/\[ 1 = 1 ] && /usr/bin/\[ 2 = 2 ] && /usr/bin/\[ 3 = 3 ]; done
real 14m8.678s
You want -a as in -f foo -a -d foo (actually that test would be false, but you get the idea).
You were close with & you just needed && as in [ -f foo ] && [ -d foo ] although that runs multiple commands rather than one.
Here is a manual page for test which is the command that [ is a link to. Modern implementations of test have a lot more features (along with the shell-builtin version [[ which is documented in your shell's manpage).
check-file(){
while [[ ${#} -gt 0 ]]; do
case $1 in
fxrsw) [[ -f "$2" && -x "$2" && -r "$2" && -s "$2" && -w "$2" ]] || return 1 ;;
fxrs) [[ -f "$2" && -x "$2" && -r "$2" && -s "$2" ]] || return 1 ;;
fxr) [[ -f "$2" && -x "$2" && -r "$2" ]] || return 1 ;;
fr) [[ -f "$2" && -r "$2" ]] || return 1 ;;
fx) [[ -f "$2" && -x "$2" ]] || return 1 ;;
fe) [[ -f "$2" && -e "$2" ]] || return 1 ;;
hf) [[ -h "$2" && -f "$2" ]] || return 1 ;;
*) [[ -e "$1" ]] || return 1 ;;
esac
shift
done
}
check-file fxr "/path/file" && echo "is valid"
check-file hf "/path/folder/symlink" || { echo "Fatal error cant validate symlink"; exit 1; }
check-file fe "file.txt" || touch "file.txt" && ln -s "${HOME}/file.txt" "/docs/file.txt" && check-file hf "/docs/file.txt" || exit 1
if check-file fxrsw "${HOME}"; then
echo "Your home is your home from the looks of it."
else
echo "You infected your own home."
fi
Why not write a function to do it?
check_file () {
local FLAGS=$1
local PATH=$2
if [ -z "$PATH" ] ; then
if [ -z "$FLAGS" ] ; then
echo "check_file: must specify at least a path" >&2
exit 1
fi
PATH=$FLAGS
FLAGS=-e
fi
FLAGS=${FLAGS#-}
while [ -n "$FLAGS" ] ; do
local FLAG=`printf "%c" "$FLAGS"`
if [ ! -$FLAG $PATH ] ; then false; return; fi
FLAGS=${FLAGS#?}
done
true
}
Then just use it like:
for path in / /etc /etc/passwd /bin/bash
{
if check_file -dx $path ; then
echo "$path is a directory and executable"
else
echo "$path is not a directory or not executable"
fi
}
And you should get:
/ is a directory and executable
/etc is a directory and executable
/etc/passwd is not a directory or not executable
/bin/bash is not a directory or not executable
This seems to work (notice the double brackets):
#!/bin/bash
if [[ -fwd "/Library/Application Support" ]]
then
echo 'YES SIR -f -w -d are fine'
else
echo 'no -f or -w or -d for you'
fi
I'm having a hard time figuring out how to do this if statement. I want to do this:
IF (the function has only 1 argument
AND $1 is a directory (in the current
folder)) OR IF (the function has 2
arguments AND $1 is NOT a directory ) THEN
....
END
Sorry if it's not very clear,
Thanks in advance
You pretty much said what is needed in the question:
if [ $# = 1 -a -d "$1" ] || [ $# = 2 -a ! -d "$1" ]
then
...
fi
You can use other operators too - that will work in Bourne shell, let alone Korn or other POSIX shells (assuming that $# works correctly in a function - which it does in Bash).
fun()
{
if [ $# = 1 -a -d "$1" ] || [ $# = 2 -a ! -d "$1" ]
then echo "Pass ($1, $#)"
else echo "Fail ($1, $#)"
fi
}
fun $HOME
fun $HOME abc
fun $HOME/xyz abc
fun /dev/null
if [[ $# == 1 && -d "$1" ]]; then
echo "one param, first is a dir"
elif [[ $# == 2 && ! -d "$1" ]]; then
echo "two params, first is not a dir"
else
echo "unexpected"
fi