Test If File Exists

How do I tell if a file does not exist in Bash?

The test command (written as [ here) has a "not" logical operator, ! (exclamation mark):

if [ ! -f /tmp/foo.txt ]; then
    echo "File not found!"
fi

How to check if a file exists in a shell script

You're missing a required space between the bracket and -e:

#!/bin/bash
if [ -e x.txt ]
then
    echo "ok"
else
    echo "nok"
fi

Test if a file exists

What you have here is a misunderstanding of where specific syntax is used. The [ -e ./documents_2019-12-12.tar.gz ] part of your command is syntax specific to the if clause in bash. Here's an example

if [ -e ./documents_2019-12-12.tar.gz ]
    then 
        echo "File Exists!"
fi

The square brackets [] are used to surround the check being performed by the if statement and the -e flag is specific to these if checks. More info here http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html

To explain the error you're seeing, the < operator takes a file to the right and feeds the contents to the command on the left. In your case the < sees the [ as the thing on the right so we try and read it as a file. Such a file doesn't exist so bash helpfully tells you that there's an error (the bash: [: No such file or directory bit) and then quits out.

How do I check if file exists in Makefile so I can delete it?

The second top answer mentions ifeq, however, it fails to mention that this ifeq must be at the same indentation level in the makefile as the name of the target, e.g., to download a file only if it doesn't currently exist, the following code could be used:

download:
ifeq (,$(wildcard ./glob.c))
    curl … -o glob.c
endif

# THIS DOES NOT WORK!
download:
    ifeq (,$(wildcard ./glob.c))
        curl … -o glob.c
    endif

Fastest way to check if a file exists using standard C++/C++11,14,17/C?

Well I threw together a test program that ran each of these methods 100,000 times, half on files that existed and half on files that didn't.

#include <sys/stat.h>
#include <unistd.h>
#include <string>
#include <fstream>

inline bool exists_test0 (const std::string& name) {
    ifstream f(name.c_str());
    return f.good();
}

inline bool exists_test1 (const std::string& name) {
    if (FILE *file = fopen(name.c_str(), "r")) {
        fclose(file);
        return true;
    } else {
        return false;
    }   
}

inline bool exists_test2 (const std::string& name) {
    return ( access( name.c_str(), F_OK ) != -1 );
}

inline bool exists_test3 (const std::string& name) {
  struct stat buffer;   
  return (stat (name.c_str(), &buffer) == 0); 
}

Results for total time to run the 100,000 calls averaged over 5 runs,

if (access(fname, F_OK) == 0) {
    // file exists
} else {
    // file doesn't exist
}

#ifdef WIN32
#include <io.h>
#define F_OK 0
#define access _access
#endif

#!/bin/bash

file="$@"
if [ -f $file ]
then 
echo "File exists"
else
echo "File does not exist"
fi

if [ ! -f /tmp/foo.txt ]; then
    echo "File not found!"
fi