I'm using a bash script to make changes to an SQL database. One of the values i'm updating uses dollar signs. The current value being something like "$$$$$" and i need to change it to "$$$$$$$$$$". However, a a $ in a bash script is used for variables.
How can i allow this small section of my bash script to used a $ as a normal character?
function prep() {
DATE_STAMP=$(date +%m%d%Y)
log "Changing mask to 10 characters"
log "$(/opt/CPU/bin/connx-query -q "update TYPE set TYPE.MASK = '$$$$$$$$$$'")"
}
As it stands right now, its just replacing each dollar sign with some random number found earlier in my script.
Bash provides different types of quoting, each with different rules about substitution (single quote ', double quote ", here document/string <<<"string" and and $'.
The double quote (used in the log ... update) will enable variable substitution, replacing each pair of $$ with the current shell PID (looks like random number).
Few options:
Consider quoting each '$' to prevent expansion
log "$(/opt/CPU/bin/connx-query -q "update TYPE set TYPE.MASK = '\$\$\$\$\$\$\$\$\$\$'")"
Over thought my own question. I can just escape the $. '\$\$\$\$\$\$\$\$\$\$'
Related
I've written a bunch of environment variables in Docker format, but now I want to use them outside of that context. How can I source them with one line of bash?
Details
Docker run and compose have a convenient facility for importing a set of environment variables from a file. That file has a very literal format.
The value is used as is and not modified at all. For example if the value is surrounded by quotes (as is often the case of shell variables), the quotes are included in the value passed
Lines beginning with # are treated as comments and are ignored
Blank lines are also ignored.
"If no = is provided and that variable is…exported in your local environment," docker "passes it to the container"
Thankfully, whitespace before the = will cause the run to fail
so, for example, this env-file:
# This is a comment, with an = sign, just to mess with us
VAR1=value1
VAR2=value2
USER
VAR3=is going to = trouble
VAR4=this $sign will mess with things
VAR5=var # with what looks like a comment
#VAR7 =would fail
VAR8= but what about this?
VAR9="and this?"
results in these env variables in the container:
user=ubuntu
VAR1=value1
VAR2=value2
VAR3=is going to = trouble
VAR4=this $sign will mess with things
VAR5=var # with what looks like a comment
VAR8= but what about this?
VAR9="and this?"
The bright side is that once I know what I'm working with, it's pretty easy to predict the effect. What I see is what I get. But I don't think bash would be able to interpret this in the same way without a lot of changes. How can I put this square Docker peg into a round Bash hole?
tl;dr:
source <(sed -E -e "s/^([^#])/export \1/" -e "s/=/='/" -e "s/(=.*)$/\1'/" env.list)
You're probably going to want to source a file, whose contents
are executed as if they were printed at the command line.
But what file? The raw docker env-file is inappropriate, because it won't export the assigned variables such that they can be used by child processes, and any of the input lines with spaces, quotes, and other special characters will have undesirable results.
Since you don't want to hand edit the file, you can use a stream editor to transform the lines to something more bash-friendly. I started out trying to solve this with one or two complex Perl 5 regular expressions, or some combination of tools, but I eventually settled on one sed command with one simple and two extended regular expressions:
sed -E -e "s/^([^#])/export \1/" -e "s/=/='/" -e "s/(=.*)$/\1'/" env.list
This does a lot.
The first expression prepends export to any line whose first character is anything but #.
As discussed, this makes the variables available to anything else you run in this session, your whole point of being here.
The second expression simply inserts a single-quote after the first = in a line, if applicable.
This will always enclose the whole value, whereas a greedy match could lop off some of (e.g.) VAR3, for example
The third expression appends a second quote to any line that has at least one =.
it's important here to match on the = again so we don't create an unmatched quotation mark
Results:
# This is a comment, with an =' sign, just to mess with us'
export VAR1='value1'
export VAR2='value2'
export USER
export VAR3='is going to = trouble'
export VAR4='this $sign will mess with things'
export VAR5='var # with what looks like a comment'
#VAR7 ='would fail'
export VAR8=' but what about this?'
export VAR9='"and this?"'
Some more details:
By wrapping the values in single-quotes, you've
prevented bash from assuming that the words after the space are a command
appropriately brought the # and all succeeding characters into the VAR5
prevented the evaluation of $sign, which, if wrapped in double-quotes, bash would have interpreted as a variable
Finally, we'll take advantage of process substitution to pass this stream as a file to source, bring all of this down to one line of bash.
source <(sed -E -e "s/^([^#])/export \1/" -e "s/=/='/" -e "s/(=.*)$/\1'/" env.list)
Et voilà!
I want to run a command from a bash script which has single quotes and some other commands inside the single quotes and a variable.
e.g. repo forall -c '....$variable'
In this format, $ is escaped and the variable is not expanded.
I tried the following variations but they were rejected:
repo forall -c '...."$variable" '
repo forall -c " '....$variable' "
" repo forall -c '....$variable' "
repo forall -c "'" ....$variable "'"
If I substitute the value in place of the variable the command is executed just fine.
Please tell me where am I going wrong.
Inside single quotes everything is preserved literally, without exception.
That means you have to close the quotes, insert something, and then re-enter again.
'before'"$variable"'after'
'before'"'"'after'
'before'\''after'
Word concatenation is simply done by juxtaposition. As you can verify, each of the above lines is a single word to the shell. Quotes (single or double quotes, depending on the situation) don't isolate words. They are only used to disable interpretation of various special characters, like whitespace, $, ;... For a good tutorial on quoting see Mark Reed's answer. Also relevant: Which characters need to be escaped in bash?
Do not concatenate strings interpreted by a shell
You should absolutely avoid building shell commands by concatenating variables. This is a bad idea similar to concatenation of SQL fragments (SQL injection!).
Usually it is possible to have placeholders in the command, and to supply the command together with variables so that the callee can receive them from the invocation arguments list.
For example, the following is very unsafe. DON'T DO THIS
script="echo \"Argument 1 is: $myvar\""
/bin/sh -c "$script"
If the contents of $myvar is untrusted, here is an exploit:
myvar='foo"; echo "you were hacked'
Instead of the above invocation, use positional arguments. The following invocation is better -- it's not exploitable:
script='echo "arg 1 is: $1"'
/bin/sh -c "$script" -- "$myvar"
Note the use of single ticks in the assignment to script, which means that it's taken literally, without variable expansion or any other form of interpretation.
The repo command can't care what kind of quotes it gets. If you need parameter expansion, use double quotes. If that means you wind up having to backslash a lot of stuff, use single quotes for most of it, and then break out of them and go into doubles for the part where you need the expansion to happen.
repo forall -c 'literal stuff goes here; '"stuff with $parameters here"' more literal stuff'
Explanation follows, if you're interested.
When you run a command from the shell, what that command receives as arguments is an array of null-terminated strings. Those strings may contain absolutely any non-null character.
But when the shell is building that array of strings from a command line, it interprets some characters specially; this is designed to make commands easier (indeed, possible) to type. For instance, spaces normally indicate the boundary between strings in the array; for that reason, the individual arguments are sometimes called "words". But an argument may nonetheless have spaces in it; you just need some way to tell the shell that's what you want.
You can use a backslash in front of any character (including space, or another backslash) to tell the shell to treat that character literally. But while you can do something like this:
reply=\”That\'ll\ be\ \$4.96,\ please,\"\ said\ the\ cashier
...it can get tiresome. So the shell offers an alternative: quotation marks. These come in two main varieties.
Double-quotation marks are called "grouping quotes". They prevent wildcards and aliases from being expanded, but mostly they're for including spaces in a word. Other things like parameter and command expansion (the sorts of thing signaled by a $) still happen. And of course if you want a literal double-quote inside double-quotes, you have to backslash it:
reply="\"That'll be \$4.96, please,\" said the cashier"
Single-quotation marks are more draconian. Everything between them is taken completely literally, including backslashes. There is absolutely no way to get a literal single quote inside single quotes.
Fortunately, quotation marks in the shell are not word delimiters; by themselves, they don't terminate a word. You can go in and out of quotes, including between different types of quotes, within the same word to get the desired result:
reply='"That'\''ll be $4.96, please," said the cashier'
So that's easier - a lot fewer backslashes, although the close-single-quote, backslashed-literal-single-quote, open-single-quote sequence takes some getting used to.
Modern shells have added another quoting style not specified by the POSIX standard, in which the leading single quotation mark is prefixed with a dollar sign. Strings so quoted follow similar conventions to string literals in the ANSI standard version of the C programming language, and are therefore sometimes called "ANSI strings" and the $'...' pair "ANSI quotes". Within such strings, the above advice about backslashes being taken literally no longer applies. Instead, they become special again - not only can you include a literal single quotation mark or backslash by prepending a backslash to it, but the shell also expands the ANSI C character escapes (like \n for a newline, \t for tab, and \xHH for the character with hexadecimal code HH). Otherwise, however, they behave as single-quoted strings: no parameter or command substitution takes place:
reply=$'"That\'ll be $4.96, please," said the cashier'
The important thing to note is that the single string that gets stored in the reply variable is exactly the same in all of these examples. Similarly, after the shell is done parsing a command line, there is no way for the command being run to tell exactly how each argument string was actually typed – or even if it was typed, rather than being created programmatically somehow.
Below is what worked for me -
QUOTE="'"
hive -e "alter table TBL_NAME set location $QUOTE$TBL_HDFS_DIR_PATH$QUOTE"
EDIT: (As per the comments in question:)
I've been looking into this since then. I was lucky enough that I had repo laying around. Still it's not clear to me whether you need to enclose your commands between single quotes by force. I looked into the repo syntax and I don't think you need to. You could used double quotes around your command, and then use whatever single and double quotes you need inside provided you escape double ones.
just use printf
instead of
repo forall -c '....$variable'
use printf to replace the variable token with the expanded variable.
For example:
template='.... %s'
repo forall -c $(printf "${template}" "${variable}")
Variables can contain single quotes.
myvar=\'....$variable\'
repo forall -c $myvar
I was wondering why I could never get my awk statement to print from an ssh session so I found this forum. Nothing here helped me directly but if anyone is having an issue similar to below, then give me an up vote. It seems any sort of single or double quotes were just not helping, but then I didn't try everything.
check_var="df -h / | awk 'FNR==2{print $3}'"
getckvar=$(ssh user#host "$check_var")
echo $getckvar
What do you get? A load of nothing.
Fix: escape \$3 in your print function.
Does this work for you?
eval repo forall -c '....$variable'
Hello I'm reading a book about bash scripting and the author says to add the following to the end of my .bashrc file. export PATH=~/bin:"$PATH" in order to execute my file from the command line by typing its name. I notice however that if I put export PATH=~/bin:$PATH I can achieve the same result. So my question is what is the difference between the one with quotes and the one without quotes? thanks.
The quotes won't hurt anything, but neither are they necessary. Assignments are processed specially by the shell. From the man page:
A variable may be assigned to by a statement of the form
name=[value]
If value is not given, the variable is assigned the null string. All values undergo tilde expansion, parameter and variable
expansion, command substitution, arithmetic expansion, and
quote removal (see EXPANSION below).
Notice that word-splitting and pathname generation are not on the list in bold. These are the two types of expansion you are trying to prevent by quoting a parameter expansion, but in this context they are not performed. The same rules apply to the assignments that are passed to the export built-in command.
You must include the variable PATH inside double quotes. So that it would handle the filepaths which has spaces but without double quotes, it won't handle the filenames which has spaces in it.
I was facing the same with trying to assign a JSON string to a variable in the terminal.
Wrap it with Single Quotes or Double Quotes
Use single quotes, if you string contains double quotes and vice-versa.
$ export TEMP_ENV='I like the "London" bridge'
$ echo $TEMP_ENV
>> I like the "London" bridge
$ export TEMP_ENV="I like the 'London' bridge"
$ echo $TEMP_ENV
>> I like the 'London' bridge
I want to run a command from a bash script which has single quotes and some other commands inside the single quotes and a variable.
e.g. repo forall -c '....$variable'
In this format, $ is escaped and the variable is not expanded.
I tried the following variations but they were rejected:
repo forall -c '...."$variable" '
repo forall -c " '....$variable' "
" repo forall -c '....$variable' "
repo forall -c "'" ....$variable "'"
If I substitute the value in place of the variable the command is executed just fine.
Please tell me where am I going wrong.
Inside single quotes everything is preserved literally, without exception.
That means you have to close the quotes, insert something, and then re-enter again.
'before'"$variable"'after'
'before'"'"'after'
'before'\''after'
Word concatenation is simply done by juxtaposition. As you can verify, each of the above lines is a single word to the shell. Quotes (single or double quotes, depending on the situation) don't isolate words. They are only used to disable interpretation of various special characters, like whitespace, $, ;... For a good tutorial on quoting see Mark Reed's answer. Also relevant: Which characters need to be escaped in bash?
Do not concatenate strings interpreted by a shell
You should absolutely avoid building shell commands by concatenating variables. This is a bad idea similar to concatenation of SQL fragments (SQL injection!).
Usually it is possible to have placeholders in the command, and to supply the command together with variables so that the callee can receive them from the invocation arguments list.
For example, the following is very unsafe. DON'T DO THIS
script="echo \"Argument 1 is: $myvar\""
/bin/sh -c "$script"
If the contents of $myvar is untrusted, here is an exploit:
myvar='foo"; echo "you were hacked'
Instead of the above invocation, use positional arguments. The following invocation is better -- it's not exploitable:
script='echo "arg 1 is: $1"'
/bin/sh -c "$script" -- "$myvar"
Note the use of single ticks in the assignment to script, which means that it's taken literally, without variable expansion or any other form of interpretation.
The repo command can't care what kind of quotes it gets. If you need parameter expansion, use double quotes. If that means you wind up having to backslash a lot of stuff, use single quotes for most of it, and then break out of them and go into doubles for the part where you need the expansion to happen.
repo forall -c 'literal stuff goes here; '"stuff with $parameters here"' more literal stuff'
Explanation follows, if you're interested.
When you run a command from the shell, what that command receives as arguments is an array of null-terminated strings. Those strings may contain absolutely any non-null character.
But when the shell is building that array of strings from a command line, it interprets some characters specially; this is designed to make commands easier (indeed, possible) to type. For instance, spaces normally indicate the boundary between strings in the array; for that reason, the individual arguments are sometimes called "words". But an argument may nonetheless have spaces in it; you just need some way to tell the shell that's what you want.
You can use a backslash in front of any character (including space, or another backslash) to tell the shell to treat that character literally. But while you can do something like this:
reply=\”That\'ll\ be\ \$4.96,\ please,\"\ said\ the\ cashier
...it can get tiresome. So the shell offers an alternative: quotation marks. These come in two main varieties.
Double-quotation marks are called "grouping quotes". They prevent wildcards and aliases from being expanded, but mostly they're for including spaces in a word. Other things like parameter and command expansion (the sorts of thing signaled by a $) still happen. And of course if you want a literal double-quote inside double-quotes, you have to backslash it:
reply="\"That'll be \$4.96, please,\" said the cashier"
Single-quotation marks are more draconian. Everything between them is taken completely literally, including backslashes. There is absolutely no way to get a literal single quote inside single quotes.
Fortunately, quotation marks in the shell are not word delimiters; by themselves, they don't terminate a word. You can go in and out of quotes, including between different types of quotes, within the same word to get the desired result:
reply='"That'\''ll be $4.96, please," said the cashier'
So that's easier - a lot fewer backslashes, although the close-single-quote, backslashed-literal-single-quote, open-single-quote sequence takes some getting used to.
Modern shells have added another quoting style not specified by the POSIX standard, in which the leading single quotation mark is prefixed with a dollar sign. Strings so quoted follow similar conventions to string literals in the ANSI standard version of the C programming language, and are therefore sometimes called "ANSI strings" and the $'...' pair "ANSI quotes". Within such strings, the above advice about backslashes being taken literally no longer applies. Instead, they become special again - not only can you include a literal single quotation mark or backslash by prepending a backslash to it, but the shell also expands the ANSI C character escapes (like \n for a newline, \t for tab, and \xHH for the character with hexadecimal code HH). Otherwise, however, they behave as single-quoted strings: no parameter or command substitution takes place:
reply=$'"That\'ll be $4.96, please," said the cashier'
The important thing to note is that the single string that gets stored in the reply variable is exactly the same in all of these examples. Similarly, after the shell is done parsing a command line, there is no way for the command being run to tell exactly how each argument string was actually typed – or even if it was typed, rather than being created programmatically somehow.
Below is what worked for me -
QUOTE="'"
hive -e "alter table TBL_NAME set location $QUOTE$TBL_HDFS_DIR_PATH$QUOTE"
EDIT: (As per the comments in question:)
I've been looking into this since then. I was lucky enough that I had repo laying around. Still it's not clear to me whether you need to enclose your commands between single quotes by force. I looked into the repo syntax and I don't think you need to. You could used double quotes around your command, and then use whatever single and double quotes you need inside provided you escape double ones.
just use printf
instead of
repo forall -c '....$variable'
use printf to replace the variable token with the expanded variable.
For example:
template='.... %s'
repo forall -c $(printf "${template}" "${variable}")
Variables can contain single quotes.
myvar=\'....$variable\'
repo forall -c $myvar
I was wondering why I could never get my awk statement to print from an ssh session so I found this forum. Nothing here helped me directly but if anyone is having an issue similar to below, then give me an up vote. It seems any sort of single or double quotes were just not helping, but then I didn't try everything.
check_var="df -h / | awk 'FNR==2{print $3}'"
getckvar=$(ssh user#host "$check_var")
echo $getckvar
What do you get? A load of nothing.
Fix: escape \$3 in your print function.
Does this work for you?
eval repo forall -c '....$variable'
How do I write a shell script (bash on HPUX) that receives a string as an argument containing an asterisk?
e.g. myscript my_db_name "SELECT * FROM table;"
The asterisk gets expanded to all the file names in the current directory, also if I assign a variable like this.
DB_QUERY="$2"
echo $DB_QUERY
The asterisk "*" is not the only character you have to watch out for, there's lots of other shell meta-charaters that can cause problems, like < > $ | ; &
The simple answer is always to put your arguments in quotes (that's the double-quote, " ) when you don't know what they might contain.
For your example, you should write:
DB_QUERY="$2"
echo "$DB_QUERY"
It starts getting awkward when you want your argument to be used as multiple parameters or you start using eval, but you can ask about that separately.
You always need to put double quotes around a variable reference if you want to prevent it from triggering filename expansion. So, in your example, use:
DB_QUERY="$2"
echo "$DB_QUERY"
In the first example, use single quotes:
myscript my_db_name 'SELECT * FROM table;'
In the second example, use double quotes:
echo "$DB_QUERY"