I like to structure if {} {} elseif {} {} in multiple lines when the statement block is rather short like below.
if {cond1} {do1}
elseif {cond2} {do2}
elseif {cond3} {do3}
But TCL doesn't let me do it. Gives : invalid command name "elseif"
It works when I open the braces around the 'do' statements into multiple line but that looks so ugly.
if {cond1} {do1
} elseif {cond2} {do2
} elseif {cond3} {do3}
What's the fundamental issue in TCL preventing it from recognizing an elseif on the next line after the if ?
Thanks,
Gert
A line break terminates the current command. To have a command continue on the next line, the newline character must be escaped or quoted.
If the newline is directly preceded by a backslash, the backslash, the newline and all tabs and spaces following in sequence will be replaced by a single space character.
if {cond1} {do1} \
elseif {cond2} {do2} \
elseif {cond3} {do3} \
else {do4}
If the newline is inside braces, it has no syntactic function. It is just another character in the string enclosed by braces and passed to the command. This is useful when you need to pass scripts consisting of several commands to e.g. an if command: the script will be re-interpreted within the command, and those newlines will resume their function there.
if {cond1} {do1
} elseif {cond2} {do2
} elseif {cond3} {do3
} else {do4}
Typical Tcl style is to write commands with script arguments like this:
if {cond1} {
do1
} elseif {cond2} {
do2
} elseif {cond3} {
do3
} else {
do4
}
This visual style isn't to everyone's taste, but one can get used to it.
Documentation: Tcl
Related
How can I remove a part of the text file if the pattern I am searching is matched?
eg:
pg_pin (VSS) {
direction : inout;
pg_type : primary_ground;
related_bias_pin : "VBN";
voltage_name : "VSS";
}
leakage_power () {
value : 0;
when : "A1&A2&X";
**related_pg_pin** : VBN;
}
My pattern is related_pg_pin. If this pattern is found i want to remove that particular section(starting from leakage power () { till the closing bracket}).
proc getSection f {
set section ""
set inSection false
while {[gets $f line] >= 0} {
if {$inSection} {
append section $line\n
# find the end of the section (a single right brace, #x7d)
if {[string match \x7d [string trim $line]]} {
return $section
}
} else {
# find the beginning of the section, with a left brace (#x7b) at the end
if {[string match *\x7b [string trim $line]]} {
append section $line\n
set inSection true
}
}
}
return
}
set f [open data.txt]
set g [open output.txt w]
set section [getSection $f]
while {$section ne {}} {
if {![regexp related_pg_pin $section]} {
puts $g $section
}
set section [getSection $f]
}
close $f
close $g
Starting with the last paragraph of the code, we open a file for reading (through the channel $f) and then get a section. (The procedure to get a section is a little bit convoluted, so it goes into a command procedure to be out of the way.) As long as non-empty sections keep coming, we check if the pattern occurs: if not, we print the section to the output file through the channel $g. Then we get the next section and go to the next iteration.
To get a section, first assume we haven't yet seen any part of a section. Then we keep reading lines until the end of the file is found. If a line ending with a left brace is found, we add it to the section and take a note that we are now in a section. From then on, we add every line to the section. If a line consisting of a single right brace is found, we quit the procedure and deliver the section to the caller.
Documentation:
! (operator),
>= (operator),
append,
close,
gets,
if,
ne (operator),
open,
proc,
puts,
regexp,
return,
set,
string,
while,
Syntax of Tcl regular expressions
Syntax of Tcl string matching:
* matches a sequence of zero or more characters
? matches a single character
[chars] matches a single character in the set given by chars (^ does not negate; a range can be given as a-z)
\x matches the character x, even if that character is special (one of *?[]\)
Here's a "clever" way to do it:
proc unknown args {
set body [lindex $args end]
if {[string first "related_pg_pin" $body] == -1} {puts $args}
}
source file.txt
Your data file appears to be Tcl-syntax-compatible, so execute it like a Tcl file, and for unknown commands, check to see if the last argument of the "command" contains the string you want to avoid.
This is clearly insanely risky, but it's fun.
In Tcl, we are using the backslash for escaping special characters as well as for spreading long commands across multiple lines.
For example, a typical if loop can be written as
set some_Variable_here 1
if { $some_Variable_here == 1 } {
puts "it is equal to 1"
} else {
puts "it is not equal to 1"
}
With the help of backslash, it can be written as follows too
set some_Variable_here 1
if { $some_Variable_here == 1 } \
{
puts "it is equal to 1"
} \
else {
puts "it is not equal to 1"
}
So, with backslash we can make the statements to be treated as if like they are in the same line.
Lets consider the set statement
I can write something like as below
set x Albert\ Einstein;# This works
puts $x
#This one is not working
set y Albert\
Einstein
If I try with double quotes or braces, then the above one will work. So, is it possible to escape the newline with backslashes without double quotes or braces?
A backslash-newline-whitespace* sequence (i.e., following whitespace is skipped over) is always replaced with a single space. To get a backslash followed by a newline in the resulting string, use \\ followed by \n instead.
set y Albert\\\nEinstein
having issues trying to debug this 'extra characters after close-brace' error. Error message points to my proc line ... I just can't see it for 2 days!
# {{{ MAIN PROGRAM
proc MAIN_PROGRAM { INPUT_GDS_OASIS_FILE L CELL_LIST_FILE } {
if { [file exists $CELL_LIST_FILE] == 0 } {
set celllist [$L cells]
} else {
set fp [open $CELL_LIST_FILE r]
set file_data [read $fp]
close $fp
set celllist [split $file_data "\n"]
set totalcells [expr [llength $celllist] - 1]
}
set counter 0
foreach cell $celllist {
set counter [expr {$counter + 1}]
set value [string length $cell]
set value3 [regexp {\$} $cell]
if { $value > 0 && $value2 == 0 && $value3 == 0 } {
# EXTRACT BOUNDRARY SIZE FIRST
puts "INFO -- READING Num : $counter/$totalcells -- $cell ..."
ONEIP_EXTRACT_BOUNDARY_SIZE $cell $L "IP_SIZE/$cell.txt"
exec gzip -f "IP_SIZE/$cell.txt"
}
}
# }}}
}
# }}}
This seems to be an unfortunate case of using braces in comments. The Tcl parser looks at braces before comments (http://tcl.tk/man/tcl8.5/TclCmd/Tcl.htm). It is a problem if putting braces in comments causes a mismatched number of open/close braces.
Try using a different commenting style, and remove the "{{{" and "}}}" from your comments.
I'm pretty sure that this is down to braces in comments within the proc body.
The wiki page here has a good explaination. In short a Tcl comment isn't like a comment most other languages and having unmatched braces in them leads to all
sorts of issues.
So the braces in the #}}} just before the end of the proc are probably the problem.
Tcl requires procedure bodies to be brace-balanced, even within comments.
OK, that's a total lie. Tcl really requires brace-quoted strings to be brace-balanced (Tcl's brace-quoted strings are just like single-quoted strings in bash, except they nest). The proc command just interprets its third argument as a script (used to define the procedure body) and it's very common to use brace-quoted strings for that sort of thing. This is a feature of Tcl's general syntax, and is why Tcl is very good indeed at handling things like DSLs.
You could instead do this:
proc brace-demo args "puts hi; # {{{"
brace-demo do it yeah
and that will work fine. Totally legal Tcl, and has a comment in a procedure body with unbalanced braces. It just happens that for virtually any real procedure, putting in all the required backslashes to stop interpretation of variable and command substitutions too soon is a total bear. Everyone uses braces for simplicity, and so has to balance them.
It's hardly ever a problem except occasionally for comments.
I'm relatively new in TCL, in TCL prompt, when we invoke a proc with some return value, the proc's return value is echoed back by tcl. Is there a way to stop it (without affecting puts or similar functionality) as an example
bash$ tclsh
% proc a {} { puts "hello"; return 34; }
% a
hello
34
%
Now how do i suppress the 34 coming to the screen? Any help is appreciated.
Update:
Actually the proc is a part of another tool, earlier it did not have any return value, but now conditionally it can return a value.
it can be called from a script and there won't be any problem (as Bryan pointed out). and it can be called from interactive prompt, then after all the necessary outputs, the return value is getting printed unnecessarily.
So 1) I don't have the facility of changing a user's tclshrc 2) existing scripts should continue to work.
And it seems strange that every time the proc is called, after all the necessary outputs, a number gets printed. To a user, this is a needless information unless he has caught the value and wants to do something. So i wanted the value to be delivered to user, but without getting printed to prompt/UI (hope i'm clear )
The interactive shell code in tclsh and wish will print any non-empty result. To get nothing printed, you have to have the last command on the “line” produce an empty result. But which command to use?
Many commands will produce an empty result:
if 1 {}
subst ""
format ""
However, the shortest is probably:
list
Thus, you could write your code like:
a;list
Of course, this only really becomes useful when your command actually produces a large result that you don't want to see. In those cases, I often find that it is most useful to use something that measures the size of the result, such as:
set tmp [something_which_produces a_gigantic result]; string length $tmp
The most useful commands I find for that are string length, llength and dict size.
If you absolutely must not print the result of the command, you have to write your own interactive loop. There are two ways to do this, depending on whether you are running inside the event loop or not:
Without the event loop
This simplistic version just checks to see if the command name is in what the user typed. It's probably not a good idea to arbitrarily throw away results otherwise!
set accum ""
while {[gets stdin line] >= 0} {
append accum $line "\n"
if {[info complete $accum]} {
if {[catch $accum msg]} {
puts stderr $msg
} elseif {$msg ne "" && ![string match *TheSpecialCommand* $accum]} {
puts $msg
}
set accum ""
}
}
With the event loop
This is just handling the blocking IO case; that's the correct thing when input is from a cooked terminal (i.e., the default)
fileevent stdin readable handleInput
set accum ""
proc handleInput {} {
global accum
if {[gets stdin line] < 0} {
exit; # Or whatever
}
append accum $line "\n"
if {[info complete $accum]} {
if {[catch {uplevel "#0" $accum} msg]} {
puts stderr $msg
} elseif {$msg ne "" && ![string match *TheSpecialCommand* $accum]} {
puts $msg
}
set accum ""
}
}
vwait forever; # Assuming you're not in wish or have some other event loop...
How to detect the command is being executed
The code above uses ![string match *TheSpecialCommand* $accum] to decide whether to throw away the command results, but this is very ugly. A more elegant approach that leverages Tcl's own built-in hooks is to use an execution trace to detect whether the command has been called (I'll just show the non-event-loop version here, for brevity). The other advantage of this is that it is simple to extend to suppressing the output from multiple commands: just add the trace to each of them.
trace add execution TheSpecialCommand enter SuppressOutput
proc SuppressOutput args {
# Important; do not suppress when it is called inside another command
if {[info level] == 1} {
set ::SuppressTheOutput 1
}
}
# Mostly very similar from here on
set accum ""
while {[gets stdin line] >= 0} {
append accum $line "\n"
if {[info complete $accum]} {
set SuppressTheOutput 0; # <<<<<< Note this!
if {[catch $accum msg]} {
puts stderr $msg
} elseif {$msg ne "" && !$SuppressTheOutput} { # <<<<<< Note this!
puts $msg
}
set accum ""
}
}
To be clear, I wouldn't ever do this in my own code! I'd just suppress the output manually if it mattered.
You could make an empty procedure in .tclshrc...
proc void {} {}
...and when you don't need a return value, end the line with ;void.
Use tcl_interactive variable to enable the return of of the value, although I'm not sure where this would be useful...
proc a {} {
puts "hello"
if { [info exist tcl_interactive] } {
return {};
} else {
return 34;
}
}
I am new to TCL and seeking a help to deal with the following expression.
I am getting the i/p string from the user to validate any of these strings below & no others in a line in CLI using procedure
{ GHI GII GJI GKI}
and another tricky one is to write regexp to match only the characters which begin with alphabet A & end with B, It also have 1 or more of either YO or OY in between using procedure.
Thank you
If that's your input, then really there's no need to use regular expressions: just check that a supplied word is in that list:
set input { GHI GII GJI GKI}
foreach word {GJI GLI} {
if {$word in $input} {
puts "$word is in [list $input]"
} else {
puts "$word is not in [list $input]"
}
}
A regex that matches "begin with alphabet A & end with B, It also have 1 or more of either YO or OY in between":
set re {^A(?:YO|OY)+B$}
foreach word {AYOB AYOOYB AYYB} {
if {[regexp $re $word]} {
puts "$word matches"
} else {
puts "$word does not match"
}
}
If you mean "either (1 or more of YO) or (1 or more of OY), then the regex is
set re {^A(?:(?:YO)+|(?:OY)+)B$}