I am taking baby steps at learning bash and I am developing a piece of code which takes an input and checks if it contains any spaces. The idea is that the variable should NOT contain any spaces and the code should consequently echo a suitable message.
Try this:
#!/bin/bash
if [[ $1 = *[[:space:]]* ]]
then
echo "space exist"
fi
You can use grep, like this:
echo " foo" | grep '\s' -c
# 1
echo "foo" | grep '\s' -c
# 0
Or you may use something like this:
s=' foo'
if [[ $s =~ " " ]]; then
echo 'contains space'
else
echo 'ok'
fi
You can test simple glob patterns in portable shell by using case, without needing any external programs or Bash extensions (that's a good thing, because then your scripts are useful to more people).
#!/bin/sh
case "$1" in
*' '*)
printf 'Invalid argument %s (contains space)\n' "$1" >&2
exit 1
;;
esac
You might want to include other whitespace characters in your check - in which case, use *[[:space:]]* as the pattern instead of *' '*.
You can use wc -w command to check if there are any words. If the result of this output is a number greater than 1, then it means that there are more than 1 words in the input. Here's an example:
#!/bin/bash
read var1
var2=`echo $var1 | wc -w`
if [ $var2 -gt 1 ]
then
echo "Spaces"
else
echo "No spaces"
fi
Note: there is a | (pipe symbol) which means that the result of echo $var1 will be given as input to wc -w via the pipe.
Here is the link where I tested the above code: https://ideone.com/aKJdyN
You could use parameter expansion to remove everything that isn't a space and see if what's left is the empty string or not:
var1='has space'
var2='nospace'
for var in "$var1" "$var2"; do
if [[ ${var//[^[:space:]]} ]]; then
echo "'$var' contains a space"
fi
done
The key is [[ ${var//[^[:space:]]} ]]:
With ${var//[^[:space:]]}, everything that isn't a space is removed from the expansion of $var.
[[ string ]] has a non-zero exit status if string is empty. It's a shorthand for the equivalent [[ -n string ]].
We could also quote the expansion of ${var//[^[:space:]]}, but [[ ... ]] takes care of the quoting for us.
Related
I want to ensure that the given arguments are flags, by which I mean -x where x is some character or sequence of.
I have tried to do this with the following:
if [[ "$(echo '$1' | sed 's/[^-]//g')" -ne "-" ]];
then
echo "$usage"
exit
fi
Where my reasoning is that if - is not present when other characters are stripped it's not a flag.
This doesn't work though, and is obviously flimsy, but I don't know how to do this correctly.
# valid
script.sh -asdf
# invalid
script.sh sdf
You can do it this way to make sure $1 is starting with -:
if [[ "${1?}" != -* ]]; then
echo "$usage"
exit 1
fi
${1?} will fail the script if $1 is not available.
I tried to check the following case:
#!/bin/bash
line="abc"
if [[ "${line}" != [a-z] ]]; then
echo INVALID
fi
And I get INVALID as output. But why?
It's no check if $line contains only a characters in the range [a-z] ?
Use the regular expression matching operator =~:
#!/bin/bash
line="abc"
if [[ "${line}" =~ [^a-zA-Z] ]]; then
echo INVALID
fi
Works in any Bourne shell and wastes no pipes/forks:
case $var in
("") echo "empty";;
(*[!a-z]*) echo "contains a non-alphabetic";;
(*) echo "just alphabetics";;
esac
Use [!a-zA-Z] if you want to allow upper case as well.
Could you please try following and let me know if this helps you.
line="abc"
if echo "$line" | grep -i -q '^[a-z]*$'
then
echo "MATCHED."
else
echo "NOT-MATCHED."
fi
Pattern matches are anchored to the beginning and end of the string, so your code checks if $line is not a single lowercase character. You want to match an arbitrary sequence of lowercase characters, which you can do using extended patterns:
if [[ $line != #([a-z]) ]]; then
or using the regular-expression operator:
if ! [[ $line =~ ^[a-z]+$ ]]; then # there is no negative regex operator like Perl's !~
Why? Because != means "not equal", thats why. You tell bash to compare abc with [a-z]. They are not equal.
Try echo $line | grep -i -q -x '[a-z]*'.
The flag -i makes grep case insensitive.
The flag -x means match the whole line.
The flag -q means print nothing to stdout, just return 1 or 0.
I have next string comparison in bash:
if [[ $1 == "/"* ]]; then echo YES; else echo "$1"; fi
How to do same in sh?
You could do it with a case statement.
case $1 in
/*) echo YES;;
*) echo $1
esac
The direct translation would be if [ "$1" = "/*" ], but it wouldn't work because sh doesn't support glob matches there. You'd need to invoke an external command like grep.
if printf '%s\n' "$1" | grep -e '^/' >/dev/null 2>&1; then
...
fi
This would be shorter with grep -q, but if you don't have bash then you may not have grep -q either.
The case statement handles this elegantly.
case $1 in
'/'* ) echo YES;;
*) echo "$1";;
esac
The lack of quoting before in and the general syntax with the double semicolons and unpaired right parentheses is jarring to the newcomer, but you quickly get used to it. It's quite versatile and much under-appreciated.
If you insist on using [ you could perhaps do something like
if temp=${1#?}; [ "${1%$temp}" -eq '*' ]; then
...
which uses a couple of parameter expansions to extract the first character of the variable; but case has glob pattern matching built in, so it's considerably more readable.
If you would like to match a pattern, or regex in if statements if sh or fish you can use
if echo "$1" | grep -q ^/; then echo yes; else echo "$1"; fi
I want to check if a file contains a specific string or not in bash. I used this script, but it doesn't work:
if [[ 'grep 'SomeString' $File' ]];then
# Some Actions
fi
What's wrong in my code?
if grep -q SomeString "$File"; then
Some Actions # SomeString was found
fi
You don't need [[ ]] here. Just run the command directly. Add -q option when you don't need the string displayed when it was found.
The grep command returns 0 or 1 in the exit code depending on
the result of search. 0 if something was found; 1 otherwise.
$ echo hello | grep hi ; echo $?
1
$ echo hello | grep he ; echo $?
hello
0
$ echo hello | grep -q he ; echo $?
0
You can specify commands as an condition of if. If the command returns 0 in its exitcode that means that the condition is true; otherwise false.
$ if /bin/true; then echo that is true; fi
that is true
$ if /bin/false; then echo that is true; fi
$
As you can see you run here the programs directly. No additional [] or [[]].
In case if you want to check whether file does not contain a specific string, you can do it as follows.
if ! grep -q SomeString "$File"; then
Some Actions # SomeString was not found
fi
In addition to other answers, which told you how to do what you wanted, I try to explain what was wrong (which is what you wanted.
In Bash, if is to be followed with a command. If the exit code of this command is equal to 0, then the then part is executed, else the else part if any is executed.
You can do that with any command as explained in other answers: if /bin/true; then ...; fi
[[ is an internal bash command dedicated to some tests, like file existence, variable comparisons. Similarly [ is an external command (it is located typically in /usr/bin/[) that performs roughly the same tests but needs ] as a final argument, which is why ] must be padded with a space on the left, which is not the case with ]].
Here you needn't [[ nor [.
Another thing is the way you quote things. In bash, there is only one case where pairs of quotes do nest, it is "$(command "argument")". But in 'grep 'SomeString' $File' you have only one word, because 'grep ' is a quoted unit, which is concatenated with SomeString and then again concatenated with ' $File'. The variable $File is not even replaced with its value because of the use of single quotes. The proper way to do that is grep 'SomeString' "$File".
Shortest (correct) version:
grep -q "something" file; [ $? -eq 0 ] && echo "yes" || echo "no"
can be also written as
grep -q "something" file; test $? -eq 0 && echo "yes" || echo "no"
but you dont need to explicitly test it in this case, so the same with:
grep -q "something" file && echo "yes" || echo "no"
##To check for a particular string in a file
cd PATH_TO_YOUR_DIRECTORY #Changing directory to your working directory
File=YOUR_FILENAME
if grep -q STRING_YOU_ARE_CHECKING_FOR "$File"; ##note the space after the string you are searching for
then
echo "Hooray!!It's available"
else
echo "Oops!!Not available"
fi
grep -q [PATTERN] [FILE] && echo $?
The exit status is 0 (true) if the pattern was found; otherwise blankstring.
if grep -q [string] [filename]
then
[whatever action]
fi
Example
if grep -q 'my cat is in a tree' /tmp/cat.txt
then
mkdir cat
fi
In case you want to checkif the string matches the whole line and if it is a fixed string, You can do it this way
grep -Fxq [String] [filePath]
example
searchString="Hello World"
file="./test.log"
if grep -Fxq "$searchString" $file
then
echo "String found in $file"
else
echo "String not found in $file"
fi
From the man file:
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings, separated by newlines, any of
which is to be matched.
(-F is specified by POSIX.)
-x, --line-regexp
Select only those matches that exactly match the whole line. (-x is specified by
POSIX.)
-q, --quiet, --silent
Quiet; do not write anything to standard output. Exit immediately with zero
status if any match is
found, even if an error was detected. Also see the -s or --no-messages
option. (-q is specified by
POSIX.)
Try this:
if [[ $(grep "SomeString" $File) ]] ; then
echo "Found"
else
echo "Not Found"
fi
I done this, seems to work fine
if grep $SearchTerm $FileToSearch; then
echo "$SearchTerm found OK"
else
echo "$SearchTerm not found"
fi
grep -q "something" file
[[ !? -eq 0 ]] && echo "yes" || echo "no"
I'm writing a script that asks the user for several options and then, via a series of echo statements, creates and writes to a separate script file. That script will also be dependent on at least one command line argument when executed.
Given the original statement
if [ "` echo $1 | egrep ^[[:digit:]]+$`" = "" ]
that determines if the first argument ($1) is an integer, how can I include that in the echo statement to be written to the new file while maintaining the command line argument access?
I tried to escape the double quotes and dollar signs like
echo "if [ \"` echo \$1 | egrep ^[[:digit:]]+\$`\" = \"\" ]" >> generatePanos
but that just resulted in
if [ "" = "" ]
However, echo "\$1" results in $1 being printed in the file.
Since you are using bash, you can use bash's builtin regex:
if [[ $1 =~ ^[[:digit:]]+$ ]]; then
...
fi
Even without bash's builtin regex, there is no need for the test command ( [ ), or echo:
if grep -q -E '^[[:digit:]]+$' <<< "$1"; then
...
fi
If this must also work on shells other than bash, then you can keep the echo:
if echo "$1" | grep -q -E '^[[:digit:]]+$'; then
...
fi
The last two work because if tests the exit status of a command. The grep command returns non-zero if a match is not found.
I'm not entirely certain what you mean, but here are two things you can try:
If you're trying to print the entire line as-is (including the $1), use single-quotes to tell echo to not interpret anything:
$ echo 'if [ "` echo $1 | egrep ^[[:digit:]]+$`" = "" ]'
if [ "` echo $1 | egrep ^[[:digit:]]+$`" = "" ]
If you're trying to print the entire line but substitute in the current value for $1:
$ echo "if [ \"\` echo $1 | egrep ^[[:digit:]]+\$\`\" = \"\" ]"
if [ "` echo <<some value>> | egrep ^[[:digit:]]+$`" = "" ]
If you're trying to substitute the entire portion of the command that's in backticks (evaluated using the current value of $1), it's probably best to use an intermediate variable:
temp=$(echo $1 | egrep ^[[:digit:]]+$)
echo "if [ \"$temp\" = \"\" ]"
put a back slash before every offending character: echo if [ \"` echo $1 \| egrep ^[[:digit:]]+$`\" = \"\" ]
echo "\$1" should do exactly what you said it did.
To echo the CONTENTS of '1' then echo $1 (without the backslash).
When using variables in bash scripts, it's often good practice to double quote them (echo "$1", func_name "$1", etc) or to escape them ( echo "${1}" ).
As to the first part, are you wanting to echo the entire 'if' statement to the file? That's what it looks like. If not, then you should do this:
if [ conditions ]; then echo "$1" >> $filename