Check out this link
If you are generating the files and you can choose a file name my suggestion is to pad the number with zeros. The following function helps with that:
numstring(x, n=3) = string(x + 10^n)[2:end]
So in your case,
julia> fnames = "file_" .* numstring.(1:13, 3)
13-element Array{String,1}:
"file_001"
"file_002"
"file_003"
"file_004"
"file_005"
"file_006"
"file_007"
"file_008"
"file_009"
"file_010"
"file_011"
"file_012"
"file_013"
In the link above, Palli suggests the following procedure:
julia> split(read(`ls -1v`, String))
19-element Array{SubString{String},1}:
"file_1"
"file_2"
"file_3"
"file_4"
"file_5"
"file_6"
"file_7"
"file_8"
"file_9"
"file_10"
"file_11"
"file_12"
"file_13"
"file_14"
"file_15"
"file_16"
"file_18"
"file_20"
"file_25"